Chapter 7-1 Atomic Layer Deposition (ALD) Definition of ALD Brief history of ALD ALD process and equipments ALD applications 1 Definition of ALD ALD is a method of applying thin films to various substrates with atomic scale precision. Similar in chemistry to chemical vapor deposition (CVD), except that the ALD reaction breaks the CVD reaction into two half- reactions, keeping the precursor materials separate during the reaction. ALD film growth is self-limited limited and based on surface reactions, which makes achieving atomic scale deposition control possible. By keeping the precursors separate throughout the coating process, atomic layer thickness control of film grown can be obtained as fine as atomic/molecular scale per monolayer. 2 Ref: "Atomic Layer Deposition," Wikipedia: : The Free Encyclopedia, Wikimedia Foundation, 24 April 06. <http:// http://en.wikipedia.org/wiki/atomic_layer_deposition>.
Definition of ALD 3 ALD is a method of applying thin films to various substrates with atomic scale precision. Similar in chemistry to CVD, except that the ALD reaction breaks the CVD reaction into two half-reactions, keeping the precursor materials separate during the reaction. ALD film growth is self-limited limited and based on surface reactions, which makes achieving atomic scale deposition control possible. By keeping the precursors separate throughout the coating process, atomic layer thickness control of film grown can be obtained as fine as atomic/molecular scale per monolayer. Ref: "Atomic Layer Deposition," Wikipedia: : The Free Encyclopedia, Wikimedia Foundation, 24 April 06. <http:// http://en.wikipedia.org/wiki/atomic_layer_deposition>. Definition of ALD 4 ALD is a method of applying thin films to various substrates with atomic scale precision. Similar in chemistry to chemical vapor deposition (CVD), except that the ALD reaction breaks the CVD reaction into two half- reactions, keeping the precursor materials separate during the reaction. ALD film growth is self-limited and based on surface reactions, which makes achieving atomic scale deposition control possible. By keeping the precursors separate throughout the coating process, atomic layer thickness control of film grown can be obtained as fine as atomic/molecular scale per monolayer. Ref: "Atomic Layer Deposition," Wikipedia: : The Free Encyclopedia, Wikimedia Foundation, 24 April 06. <http:// http://en.wikipedia.org/wiki/atomic_layer_deposition>.
Definition of ALD 5 ALD is a method of applying thin films to various substrates with atomic scale precision. Similar in chemistry to chemical vapor deposition (CVD), except that the ALD reaction breaks the CVD reaction into two half- reactions, keeping the precursor materials separate during the reaction. ALD film growth is self-limited limited and based on surface reactions, which makes achieving atomic scale deposition control possible. By keeping the precursors separate throughout the coating process, atomic layer thickness control of film grown can be obtained as fine as atomic/molecular scale per monolayer. Ref: "Atomic Layer Deposition," Wikipedia: : The Free Encyclopedia, Wikimedia Foundation, 24 April 06. <http:// http://en.wikipedia.org/wiki/atomic_layer_deposition>. Brief History of ALD Introduced in 1974 by Dr. Tuomo Suntola and co-workers in Finland to improve the quality of ZnS films used in electroluminescent displays. Recently, it turned out that ALD also produces outstanding dielectric layers and attracts semiconductor industries for making High-K K dielectric materials. 6 Ref: "History of Atomic Layer Deposition (ALD)," Finnish MicroNanoTechnology Network (FMNT), 24 April 2006. <http:// http://www.fmnt.fi/index.pl?id=2913&isa=category&op=show>.
Brief History of ALD 7 Introduced in 1974 by Dr. Tuomo Suntola and co-workers in Finland to improve the quality of ZnS films used in electroluminescent displays. Recently, it turned out that ALD method also produces outstanding dielectric layers and attracted semiconductor industries for making High-K K dielectric materials. Ref: "History of Atomic Layer Deposition (ALD)," Finnish MicroNanoTechnology Network (FMNT), 24 April 2006. <http:// http://www.fmnt.fi/index.pl?id=2913&isa=category&op=show>. 8 Releases sequential precursor gas pulses to deposit a film one layer at a time on the substrate. The precursor gas is introduced into the process chamber and produces a monolayer of gas on the wafer surface. A second precursor of gas s is then introduced into the chamber reacting with the first precursor to produce a monolayer of film on the wafer surface. Example: ALD cycle for Al 2 O 3 deposition Since each pair of gas pulses (one cycle) produces exactly one monolayer m of film, the thickness of the resulting film may be precisely controlled by the number of deposition cycles. Ref: A. Knop Gericke Gericke,, "Preparation of Model Systems by Physical Methods," a lecture given at Modern Methods in Heterogeneous Catalysis Research Lecture Series, Fritz Haber Institute of the Max Planck Society. 24 April 06. <http://w3.rz-berlin.mpg.de/%7ejentoft/lehre/catalysis0405.html>.
Atomic Layer Deposition (ALD) Advantages of ALD: VERY thin films are possible as thin as 0.5-1Å (a single atomic thickness) more practically, 10-50Å 100% (perfect) step coverage over aspect ratios as high as 60:1 (DRAM trench capacitors) bottoms and sidewalls of vias and trenches are covered uniformly unequaled coverage of sharp corners Higher quality films Very low nonuniformity ( < 3% 1σ ) Lower leakage Improved reliability 9 Atomic Layer Deposition (ALD) Advantages of ALD (continued): Low consummable usage due to thinner film requirements Lower required substrate temperature allowing improved thermal budget compatibility 10
Atomic Layer Deposition (ALD) Disadvantages of ALD: Slow throughput debatable because the films are so thin some manufacturers are developing batch processing ALD tools others are working on higher-throughput alternatives High capital cost of tools may be offset somewhat because cost of ownership (COO) may be less Difficult to control contamination in films slow deposition rate allows plenty of time for impurities to incorporate in the film 11 A first precursor gas is introduced into the process chamber and produces a monolayer of gas on the wafer surface. Then a second precursor of gas is introduced into the chamber reacting with the first precursor to produce a monolayer of film on the wafer surface. Example: ALD cycle for Al 2 O 3 deposition Since each pair of gas pulses (one cycle) produces exactly one monolayer m of film, the thickness of the resulting film may be precisely controlled by the t number of deposition cycles. Ref: A. Knop Gericke Gericke,, "Preparation of Model Systems by Physical Methods," a lecture given at Modern Methods in Heterogeneous Catalysis Research Lecture Series, Fritz Haber Institute of the Max Planck Society. 24 April 06. <http://w3.rz-berlin.mpg.de/%7ejentoft/lehre/catalysis0405.html>. 12
A first precursor gas is introduced into the process chamber and produces a monolayer of gas on the wafer surface. Then a second precursor of gas is introduced into the chamber reacting with the first precursor to produce a monolayer of film on the wafer surface. Example: ALD cycle for Al 2 O 3 deposition (Step 1a) 13 Ref: "Atomic Layer Deposition," Cambridge NanoTech Inc., 24 April 06. <http:// < http://www.cambridgenanotech.com/>. A first precursor gas is introduced into the process chamber and produces a monolayer of gas on the wafer surface. Then a second precursor of gas is introduced into the chamber reacting with the first precursor to produce a monolayer of film on the wafer surface. Example: ALD cycle for Al 2 O 3 deposition (Step 1b) 14 Ref: "Atomic Layer Deposition," Cambridge NanoTech Inc., 24 April 06. <http:// < http://www.cambridgenanotech.com/>.
A first precursor gas is introduced into the process chamber and produces a monolayer of gas on the wafer surface. Then a second precursor of gas is introduced into the chamber reacting with the first precursor to produce a monolayer of film on the wafer surface. Example: ALD cycle for Al 2 O 3 deposition (Step 1c) 15 Ref: "Atomic Layer Deposition," Cambridge NanoTech Inc., 24 April 06. <http:// < http://www.cambridgenanotech.com/>. A first precursor gas is introduced into the process chamber and produces a monolayer of gas on the wafer surface. Then a second precursor of gas is introduced into the chamber reacting with the first precursor to produce a monolayer of film on the wafer surface. Example: ALD cycle for Al 2 O 3 deposition (Step 2a) 16 Ref: "Atomic Layer Deposition," Cambridge NanoTech Inc., 24 April 06. <http:// < http://www.cambridgenanotech.com/>.
A first precursor gas is introduced into the process chamber and produces a monolayer of gas on the wafer surface. Then a second precursor of gas is introduced into the chamber reacting with the first precursor to produce a monolayer of film on the wafer surface. Example: ALD cycle for Al 2 O 3 deposition (Step 2b) 17 Ref: "Atomic Layer Deposition," Cambridge NanoTech Inc., 24 April 06. <http:// < http://www.cambridgenanotech.com/>. A first precursor gas is introduced into the process chamber and produces a monolayer of gas on the wafer surface. Then a second precursor of gas is introduced into the chamber reacting with the first precursor to produce a monolayer of film on the wafer surface. Example: ALD cycle for Al 2 O 3 deposition (Step 2c) 18 Ref: "Atomic Layer Deposition," Cambridge NanoTech Inc., 24 April 06. <http:// < http://www.cambridgenanotech.com/>.
A first precursor gas is introduced into the process chamber and produces a monolayer of gas on the wafer surface. Then a second precursor of gas is introduced into the chamber reacting with the first precursor to produce a monolayer of film on the wafer surface. Example: ALD cycle for Al 2 O 3 deposition (after 3 cycles) 19 Ref: "Atomic Layer Deposition," Cambridge NanoTech Inc., 24 April 06. <http:// < http://www.cambridgenanotech.com/>. 20 A first precursor gas is introduced into the process chamber and produces a monolayer of gas on the wafer surface. Then a second precursor of gas is introduced into the chamber reacting with the first precursor to produce a monolayer of film on the wafer surface. Example: ALD cycle for Al 2 O 3 deposition Since each pair of gas pulses (one cycle) produces exactly one monolayer of film, the thickness of the resulting film may be precisely controlled by the number of deposition cycles. Ref: "Technology Backgrounder: Atomic Layer Deposition," IC Knowledge e LLC, 24 April 06. <www.icknowledge.com/misc_technology/atomic%20layer%20deposition% www.icknowledge.com/misc_technology/atomic%20layer%20deposition%20briefing.pdf>. Step coverage and deposition rate Vs. deposition technique.
21 Four main types of ALD reactors Closed system chambers Open system chambers Semi-closed system chambers Semi-open system chambers 22 Four main types of ALD reactors Closed system chambers (most common) Open system chambers Semi-closed system chambers Semi-open system chambers
23 Four main types of ALD reactors Closed system chambers (most common) The reaction chamber walls are designed to effect the transport of the precursors. Schematic of a closed ALD system Open system chambers Semi-closed system chambers Semi-open system chambers Ref: "Technology Backgrounder: Atomic Layer Deposition," IC Knowledge e LLC, 24 April 06. <www.icknowledge.com/misc_technology/atomic%20layer%20deposition% www.icknowledge.com/misc_technology/atomic%20layer%20deposition%20briefing.pdf>. 24 [1] [1] The Verano 5500 A 300-mm ALD system by Aviza Technology, Inc [2]. Process Temperature [1] 1 "Technology Backgrounder: Atomic Layer Deposition," IC Knowledge e LLC, 24 April 06. <www.icknowledge.com/misc_technology/atomic%20layer%20deposition% www.icknowledge.com/misc_technology/atomic%20layer%20deposition%20briefing.pdf> 2 Atomic Layer Deposition," Aviza Technology. 26 April 06. <http:// http://www.avizatechnology.com/products/verano.shtml>. >.
25 One cycle [1] [1] The Verano 5500 A 300-mm ALD system by Aviza Technology, Inc [2]. Acceptable temperature range for deposition. Process Temperature [1] 1 "Technology Backgrounder: Atomic Layer Deposition," IC Knowledge e LLC, 24 April 06. <www.icknowledge.com/misc_technology/atomic%20layer%20deposition% www.icknowledge.com/misc_technology/atomic%20layer%20deposition%20briefing.pdf>. >. 2 Atomic Layer Deposition," Aviza Technology. 26 April 06. <http:// http://www.avizatechnology.com/products/verano.shtml>. >. ALD Precursor Requirements Must be volatile and thermally stable Preferably liquids and gases Should Chemisorb onto the surface or rapidly react with surface and react aggressively with each other 就 是 互 斥 不 反 應 -Short saturation time, good deposition rate, no gas phase reactions Should not self-decompose - Affect thickness, uniformity Should not etch, dissolute into film or substrate 26
ALD Applications High-K K dielectrics for CMOS Semiconductor memory (DRAM) Cu interconnect barrier Deposition in porous structures 27 ALD Applications High-K K dielectrics for CMOS Semiconductor memory (DRAM) Cu interconnect barrier Deposition in porous structures 28
ALD Applications High-K K dielectrics for CMOS 29 Reduces leakage current Faster switching speed Cooler transistors Candidates for High-K K dielectrics Film Precursors Al 2 O 3 Al(CH) 3, H 2 O or O 3 HfO 2 HfCl 4 or TEMAH, H 2 O ZrO 2 ZrCl 4, H 2 O Ref: "Intel's High-k/Metal Gate Announcement," Intel Corporation. 26 April, 06. <http://www.intel.com/technology/silicon/micron.htm#high>. ALD Applications 30 High-K K dielectrics for CMOS Semiconductor memory (DRAM) Cu interconnect barrier Deposition in porous structures Step coverage and deposition rate Vs. deposition technique. All these applications take advantage of uniformity, conformal step coverage, precise thickness control of deposited films, which can be achieved by ALD deposition method. Ref: "Technology Backgrounder: Atomic Layer Deposition," IC Knowledge e LLC, 24 April 06. <www.icknowledge.com/misc_technology/atomic%20layer%20deposition% www.icknowledge.com/misc_technology/atomic%20layer%20deposition%20briefing.pdf>.
Atomic Layer Deposition (ALD) Copper Barrier Layer: Historically, TaN has been deposited via PVD Minimum thickness 100-300Å poor stoichiometry compromises effectiveness of barrier poor step coverage requires thicker film, which increases resistance of the metal line ALD TaN: as thin as 10-15Å still provides acceptable barrier effectiveness good stoichiometry Monocrystalline deposition epitaxial alignment with underlying layer 31 Comparison of ALD and CVD 32 ALD Highly reactive precursors Precursors react separately on the substrate Precursors must not decompose at process temperature Uniformity ensured by the saturation mechanism Thickness control by counting the number of reaction cycles Surplus precursor dosing acceptable CVD Less reactive precursors Precursors react at the same time on the substrate Precursors can decompose at process temperature Uniformity requires uniform flux of reactant and temperature Thickness control by precise process control and monitoring Precursor dosing important
Summary 33 Advantages Stoichiometric films with large area uniformity and 3D conformality. Precise thickness control. Low temperature deposition possible. Gentle deposition process for sensitive substrates. Disadvantages Deposition Rate slower than CVD. Number of different material that can be deposited is fair compared to MBE.