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Applications of Chemical Engineering Principles to Thin Film Deposition Process Development Collin Mui Chemical Engineering 140 Guest Lecture Stanford.

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Presentation on theme: "Applications of Chemical Engineering Principles to Thin Film Deposition Process Development Collin Mui Chemical Engineering 140 Guest Lecture Stanford."— Presentation transcript:

1 Applications of Chemical Engineering Principles to Thin Film Deposition Process Development Collin Mui Chemical Engineering 140 Guest Lecture Stanford University May 22, 2008

2 P. 2 Novellus Systems Proprietary Information Thin Film Deposition Process Development è Thin film deposition processes Chemical vapor deposition Atomic layer deposition Reactor design and applications PDL™ Oxide è Make sure it works Mechanism of thin film deposition Lesson 1: Chemical kinetics modeling è Make sure it works the same way Temperature effects on deposition Lesson 2: Heat transfer è Make sure it works the same way at high yield and low cost Defect detection and reduction Lesson 3: Particle transport Wafer TMA Silanol F drag F grav F thermo

3 P. 3 Novellus Systems Proprietary Information Thin Film Deposition Process and Applications è Chemical vapor deposition (CVD) è Films deposited by CVD SURFACE REACTION Precursor Desorption è Atomic layer deposition (ALD) Passivation SiO 2 Shallow Trench Isolation (STI) Inter Metal Dielectric (IMD) Pre Metal Dielectric (PMD) Deep Trench Isolation

4 P. 4 Novellus Systems Proprietary Information Thin Film Deposition Reactor è Chemical engineering principles è Novellus™ deposition reactor Precursor delivery Fluid dynamics Reaction kinetics Temperature control Heat transfer

5 P. 5 Novellus Systems Proprietary Information 1. Capacitor sacrificial layer Sacrificial oxide layer for subsequent etch or CMP Thickness = Å PDL™ Oxide – A Novel Technology è PDL ™ Oxide: Enabling technology Conformal insulator layer Thick films (10kÅ) possible Low temperature deposition No plasma damage è PDL ™ Oxide: Precise engineering Accurate thickness control Excellent repeatability High productivity and manufacturability 2. 3D-Interconnect: Wafer level packaging Insulating oxide liner for through wafer vias (TWVs) Large CD but high AR structures Thickness = 2000 – 10000Å 3.Lithography spacer or oxide liner Reduce CD limit of lithography Thin oxide spacer or liner film Thickness = 50Å to 700Å

6 P. 6 Novellus Systems Proprietary Information AR ~ 4.5 AR ~ 8 Conformal Film Deposition via Surface Reactions Catalytic Monolayer Surface Polymerization Surface Polymerization Surface Polymerization Silica Catalytic Monolayer Catalytic Monolayer Catalytic Monolayer Trench fill mechanism extendable to high aspect ratio structures AR ~ 17

7 P. 7 Novellus Systems Proprietary Information 300 mm Handler (WTS) PDL Module Catalyst Station Silanol Station PDL Process Module Architecture and Productivity è PDL™ process module Novellus™ Multi-Station Sequential Deposition (MSSD) architecture Processes 4 wafers at the same time Novel architecture results in high productivity and accurate control è Separation of half reactions Each station performs a half reaction Improves defect performance è Precursor delivery system Accurate and repeatable thickness control Tunable thickness with good uniformity Scalable from thin to thick films

8 P. 8 Novellus Systems Proprietary Information Surface Chemistry of the PDL Process è Sequential trimethylaluminum (TMA) and silanol exposure è One monolayer of TMA catalyzes multiple silanol insertions è Cross-linking and diffusion lead to self-limiting deposition Nucleation Surface reactions only Self-limiting process Wafer TMA Cross-Linking Diffusion limited growth Conformal gap fill Wafer Chain Insertion Sequential deposition High deposition rate Wafer Silanol

9 P. 9 Novellus Systems Proprietary Information Lesson 1 – Chemical Engineering Kinetics Nucleation Wafer TMA Cross-Linking Wafer Chain Insertion Wafer Silanol Film Chain The process can be modeled as a “consecutive reaction” RF C

10 P. 10 Novellus Systems Proprietary Information Kinetic Modeling of Consecutive Reactions è Consecutive reaction è Time-dependent concentration è Kinetic equations è Solution of differential equations è Temperature dependence

11 P. 11 Novellus Systems Proprietary Information Tuning Film Properties by Deposition Temperature è Kinetics at different temperatures WERR (100:1 HF) Thermal Oxide Temperature (°C) Wet Etch Rate Ratio WERR (100:1 HF) ~150A/cyc (Thermal Oxide)WERR (100:1 HF) ~250A/cyc (Thermal Oxide) è Process space for thickness control Deposition temperature Precursor delivery Deposition time è Tunable film properties Tunable film stress Tunable wet etch rate Deposition at low temperature Deposition at high temperature Deposition at low temperature Deposition at high temperature

12 P. 12 Novellus Systems Proprietary Information Cycle 1Cycle 2Cycle 3 Cycle 1Cycle 2Cycle 3 Lesson 2 – Wafer Heating and Heat Transfer è Importance of temperature control è Inadequate heating Temperature control Heat transfer Stable Temperature = Stable Process è Adequate heating

13 P. 13 Novellus Systems Proprietary Information Heat Transfer Mechanisms Conduction T2T2 Radiation 2, T22, T2 T1T1 1, T11, T1 k x2x2 x1x1 Thermal conductivity Pedestal-wafer gap Temperature Emissivity Convection T2T2 T1T1 u Gas velocity Gas pressure

14 P. 14 Novellus Systems Proprietary Information Heat Transfer by Convection è LPCVD Reactor Pressure = 10 mT to 10 T Gas = N 2 Final temperature = 200 °C Flow = variable è Effect of gas flow rate on convective heat transfer For typical CVD reactors, flow rate ~ 100 to 5000 sccm è Insignificant heat transfer by convection Less than 10% of the heat is transferred by convection Usually ignore convection in calculating wafer heating rate T2T2 T1T1 u

15 P. 15 Novellus Systems Proprietary Information Heat Transfer by Conduction è LPCVD Reactor Flow = 100 sccm to 10 slm Gas = N 2 Final temperature = 200 °C Pressure = variable è Effect of gas pressure on conductive heat transfer LPCVD ~ 10 mT to 1 T APCVD ~ 100 T è Conduction is the major heat transfer mechanism Mean free path of gas is short at low pressures While pressure does not affect thermal conductivity, the “effective pedestal- wafer gap” is reduced at low pressures Increasing conduction is key to effective wafer heating T2T2 T1T1 k x2x2 x1x1

16 P. 16 Novellus Systems Proprietary Information Heat Transfer by Radiation è LPCVD Reactor Flow = 500 sccm Gas = N 2 Pressure = 10 mT to 10 T Temperature = variable è Effect of temperature on radiative heat transfer CVD temperatures ~ 200°C to 700°C è Radiation is important at High temperatures, because of the fourth-power dependence Low pressures, when conduction is ineffective. (Note: radiation itself is independent on pressure) Radiative heat LOSS needs to be considered at high temperatures T2T2 T1T1

17 P. 17 Novellus Systems Proprietary Information Effective Wafer Heating by Controlling Conduction è Heat transfer by conduction High pressure – a lot of gas molecules Small pedestal-wafer gap è Improving gas conductivity Helium has higher thermal conductivity However, it is more expensive Use of “heat soak” cycle to preheat wafer to process temperature k 

18 P. 18 Novellus Systems Proprietary Information Importance of Defect Reduction è Defects in etch processes è Defects in CMP processes CD Etch CD Defect control is important in high volume manufacturing CMP

19 P. 19 Novellus Systems Proprietary Information Defect Inspection by Light Scattering è Optical system è Particle map è Light scattering signal US Patent

20 P. 20 Novellus Systems Proprietary Information Defect Analysis – Size, Shape, Composition, … è Size ~ 10  m è Size ~ 2  m è Size ~ 0.2  m Combination of “forensics” and chemical analysis techniques

21 P. 21 Novellus Systems Proprietary Information Film Accumulation and Particle Generation è Particle accumulation The goal of a CVD process is to deposit film on a wafer. Unfortunately, film also deposits on the reactor walls (hopefully at a slower rate), and the film accumulates as more wafers are deposited At some point, the accumulated film deliminates and becomes a particle source. è Particle generation CVD films are usually stressed (why?). Interface between two different materials (film and reactor wall) may be weak (adhesion, lattice mismatch) As the film deposition becomes thicker on the reactor walls, the film starts to delaminate and land on the wafer as particles. è Film delamination (and particle generation) is promoted by Interfacial stress increases with film accumulation thickness Temperature gradient and fast temperature cycling Sharp corners inside the reactor Gas flow may blow off loose particles

22 P. 22 Novellus Systems Proprietary Information Lesson 3 – Particle Transport è Particle inside CVD reactor è Forces on a particle F Drag F Grav F Thermo T1T1 T2T2 Drag force Gravitational force Thermophoretic force Drag force Gravitational force Thermophoretic force Temperature Gradient Weight Flow

23 P. 23 Novellus Systems Proprietary Information Drag Force on a Particle è Derivation of the drag force Start with fluid mechanics Drag coefficient Drag force in the continuum limit Correction for small particle at low pressures è Effect of particle size Mean free path è Effect of pressure

24 P. 24 Novellus Systems Proprietary Information Gravitational Force on a Particle è Gravitational force depends on particle size and density only Important for large particles

25 P. 25 Novellus Systems Proprietary Information Thermophoretic Force on a Particle è Thermophoretic force Particles move from surfaces at high temperatures to surfaces at low temperatures Depends on particle size Depends on temperature gradient K T is a function of particle size, mean free path, and thermal conductivities è Minimizing thermophoresis Wafer at higher temperature than the rest of the reactor è Effect of particle size è Effect of pressure Pressure and Thermophoretic Force (Size = 1  m) Temperature Gradient (K/m) Thermophoretic Force (N) 1.0E E E E E E E E E E-06 1 mT 10 mT 100 mT 1 T 10 T 100 T 760 T

26 P. 26 Novellus Systems Proprietary Information Chemical Engineering and Thin Film Deposition è Thin film deposition processes Chemical vapor deposition Atomic layer deposition Reactor design and applications PDL™ Oxide è Lesson 1: Chemical kinetics Mechanism of thin film deposition Consecutive reaction è Lesson 2: Heat transfer Temperature effects on deposition Convection, conduction, and radiation è Lesson 3: Particle transport Defect detection and reduction Particle generation mechanisms Forces on a particle Wafer TMA Silanol F drag F grav F thermo


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