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Sputtering Eyal Ginsburg WW46/02 Slide 2 Sputtering Contents Metallization structure Metallization structure PVD System Overview PVD System Overview Sputtering: yield, conditioning, methods Sputtering: yield, conditioning, methods Film nucleation and growth Film nucleation and growth Slide 3 Sputtering Contact & Metal Lines - SEM M3 M2 M1 W Plug Via 2 Silicon substrate Slide 4 Sputtering Glue Layer (Cont. 1) Slide 5 Sputtering Aluminum - General Al-alloys thin films were selected for the first 30 years of the IC industry. Al-alloys thin films were selected for the first 30 years of the IC industry. They continue to be the most widely used materials, although copper. They continue to be the most widely used materials, although copper. Al has low resistivity ( =2.7 -cm), and its compatibility with Si and SiO 2. Al has low resistivity ( =2.7 -cm), and its compatibility with Si and SiO 2. Al forms a thin native oxide (Al 2 O 3 ) on its surface upon exposure to oxygen, and affect the contact resistance. Al forms a thin native oxide (Al 2 O 3 ) on its surface upon exposure to oxygen, and affect the contact resistance. Slide 6 Sputtering Aluminum - General (cont.) Al thin films can also suffer from corrosion (ex. Al dry etch may leave chlorine residues on Al surface and lead to formation of HCl and then attack the Al). Al thin films can also suffer from corrosion (ex. Al dry etch may leave chlorine residues on Al surface and lead to formation of HCl and then attack the Al). Slide 7 Sputtering Aluminum interconnects The material used in interconnects is not pure aluminum, but an aluminum alloy. Usually with Cu (0.5-2%), sometimes with Si. The material used in interconnects is not pure aluminum, but an aluminum alloy. Usually with Cu (0.5-2%), sometimes with Si. The Cu in Al-alloy slows the electromigration (EM) phenomenon. Si slows EM slightly, used in contact level to prevent spiking. The Cu in Al-alloy slows the electromigration (EM) phenomenon. Si slows EM slightly, used in contact level to prevent spiking. Al-alloys decrease the melting point, increase the resistivity and need to be characterized (ex. Dry etch). Al-alloys decrease the melting point, increase the resistivity and need to be characterized (ex. Dry etch). Slide 8 Sputtering Metal line stack Usually the metal line contains 4-5 layers: Al - This layer makes the contacts with the Tungsten plugs. It is the primary current carrier. Al - This layer makes the contacts with the Tungsten plugs. It is the primary current carrier. TiN Layer - Creates a barrier between the Al/Cu and the Titanium layers because of the increasing temperature at a downstream process will increase the rate of the reaction of Al with Ti. TiN Layer - Creates a barrier between the Al/Cu and the Titanium layers because of the increasing temperature at a downstream process will increase the rate of the reaction of Al with Ti. Slide 9 Sputtering Metal stack (Cont. 1) Titanium Layer - Provides an alternate current path (shunt) around flaws in the primary current carrier. And thus improves electromigration characteristics. Titanium Layer - Provides an alternate current path (shunt) around flaws in the primary current carrier. And thus improves electromigration characteristics. Slide 10 Sputtering Metal stack (Cont. 2) TiN ARC Layer - This is an anti reflecting coating which aides lithography to keep control of critical dimensions and to absorb light during the resist exposure. It also functions as a hillock suppressant. TiN ARC Layer - This is an anti reflecting coating which aides lithography to keep control of critical dimensions and to absorb light during the resist exposure. It also functions as a hillock suppressant. Slide 11 Sputtering Metal stack - SEM ILD Metal line W- Via2 Metal line Al TiN Ti TiN Slide 12 PVD System Overview (Endura) Slide 13 Sputtering Endura PVD system Slide 14 Sputtering Endura standard mainframe Slide 15 Sputtering Mainframe Components Preclean Ch. Applies a light. Non selective plasma etch to the wafer before the PVD process. Preclean Ch. Applies a light. Non selective plasma etch to the wafer before the PVD process. Cooldown Ch. Cools the wafer after the PVD process. Cooldown Ch. Cools the wafer after the PVD process. Expansion Ch. (C&D) Optionally configured for PVD or other processes such as etch. Expansion Ch. (C&D) Optionally configured for PVD or other processes such as etch. Wafer orienter/degas Ch. Orients the wafer flat to a designated angle and degasses the wafer to remove water vapor before the preclean process. Wafer orienter/degas Ch. Orients the wafer flat to a designated angle and degasses the wafer to remove water vapor before the preclean process. PVD Ch. DC magnetron sputter deposition chambers for depositing materials used in interconnects metalization (ex. Al, Ti, TiN, TiW). PVD Ch. DC magnetron sputter deposition chambers for depositing materials used in interconnects metalization (ex. Al, Ti, TiN, TiW). Cassette loadlocks The starting point for wafer transfers. Accept 1 cassette with 25 wafers. Cassette loadlocks The starting point for wafer transfers. Accept 1 cassette with 25 wafers. Slide 16 Sputtering Vacuum system PVD system uses Ultra-High Vacuum (UHV) to reduce particulates and provide purer film qualities. PVD system uses Ultra-High Vacuum (UHV) to reduce particulates and provide purer film qualities. The tool uses staged vacuum regimes to achieve UHV. The tool uses staged vacuum regimes to achieve UHV. Slide 17 Sputtering Pressure regions and vacuum stages Slide 18 Sputtering PVD chambers and pumps Slide 19 Sputter deposition for ULSI Slide 20 Sputtering Sputtering General Sputtering is a term used to describe the mechanism in which atoms are ejected from the surface of a material when that surface is stuck by sufficiency energetic particles. Sputtering is a term used to describe the mechanism in which atoms are ejected from the surface of a material when that surface is stuck by sufficiency energetic particles. Alternative to evaporation. Alternative to evaporation. First discovered in 1852, and developed as a thin film deposition technique by Langmuir in 1920. First discovered in 1852, and developed as a thin film deposition technique by Langmuir in 1920. Metallic films: Al-alloys, Ti, TiW, TiN, Tantalum, Nickel, Cobalt, Gold, etc. Metallic films: Al-alloys, Ti, TiW, TiN, Tantalum, Nickel, Cobalt, Gold, etc. Slide 21 Sputtering Reasons for sputtering Use large-area-targets which gives uniform thickness over the wafer. Use large-area-targets which gives uniform thickness over the wafer. Control the thickness by Dep. time and other parameters. Control the thickness by Dep. time and other parameters. Control film properties such as step coverage (negative bias), grain structure (wafer temp), etc. Control film properties such as step coverage (negative bias), grain structure (wafer temp), etc. Sputter-cleaned the surface in vacuum prior to deposition. Sputter-cleaned the surface in vacuum prior to deposition. Slide 22 Sputtering Sputtering steps 1. Ions are generated and directed at a target. 2. The ions sputter targets atoms. 3. The ejected atoms are transported to the substrate. 4. Atoms condense and form a thin film. Slide 23 Sputtering Sputtering Coating process that involves the transport of material from the target to the wafer. Atoms from the target are ejected as a result of momentum transfer between incident ions and the target. The particles traverse the vacuum chamber and are deposited on the wafer. Slide 24 Sputtering Application of Sputtering Thin film deposition: Thin film deposition: Microelectronics Decorative coating Protective coating Etching of targets: Etching of targets: Microelectronics patterning Depth profiling microanalysis Surface treatment: Surface treatment: Hardening Corrosion treatment Slide 25 Sputtering The billiard ball model There is a probability that atom C will be ejected from the surface as a result of the surface being stuck by atom A. There is a probability that atom C will be ejected from the surface as a result of the surface being stuck by atom A. In oblique angle (45-90) there is higher probability for sputtering, which occur closer to the surface. In oblique angle (45-90) there is higher probability for sputtering, which occur closer to the surface. Slide 26 Sputtering Sputter yield Defined as the number of atoms ejected per incident ion. Defined as the number of atoms ejected per incident ion. Typically, range 0.1-3. Typically, range 0.1-3. Determines the deposition rate. Determines the deposition rate. Depends on: Depends on: 1. Target material. 2. Mass of bombarding ions. 3. Energy of the bombarding ions. 4. Direction of incidence of ions (angle). 5. Pressure Slide 27 Sputtering 1 2 Sputter yield (Cont. 1) Target materials: Al/Cu(0.5%) Grain size: 45 m Grain size: 200 m Slide 28 Sputtering Sputter yield (Cont. 2) Molecule size need to be about the same size as the sputtered material: Molecule size need to be about the same size as the sputtered material: too big cause layer deformation and yield a lot of material. too small cause layer deformation w/o ejecting atoms. Target deformation = Less uniform dep. Slide 29 Sputtering Sputter yield (Cont. 3) Ion energy Vs. sputter yield: Slide 30 Sputtering Sputter yield (Cont. 4) Sputter yield peaks at