Chemical Vapor Deposition (CVD) NANO54 Foothill College

Overview What is CVD? Types of CVD –MO-CVD, PE-CVD, etc CVD process / applications PVD process / applications CVD vs. PVD Plasma Polymerization

Family of CVD Technologies

What is CVD? Chemical vapor deposition (CVD) is a chemical process used to produce high- purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber. chemical processsemiconductor industrythin filmswafervolatileprecursorsreactdecomposeby-products

CVD Process Applications Microfabrication processes widely use CVD to deposit materials in various forms, including: monocrystalline, polycrystalline, amorphous, and epitaxial. These materials include: silicon, carbon fiber, carbon nanofibers, filaments, carbon nanotubes, SiO 2, silicon-germanium, tungsten, silicon carbide, silicon nitride, silicon oxynitride, titanium nitride, and various high-k dielectrics. The CVD process is also used to produce synthetic diamonds.Microfabricationmonocrystallinepolycrystalline amorphousepitaxialsiliconcarbon fibercarbon nanofibersfilamentscarbon nanotubes SiO 2silicon-germaniumtungstensilicon carbidesilicon nitridesilicon oxynitride titanium nitridehigh-k dielectrics synthetic diamonds

What is CVD Process? Chemical Vapor Deposition is the formation of a non- volatile solid film on a substrate by the reaction of vapor phase chemicals (reactants) that contain the required constituents. The reactant gases are introduced into a reaction chamber and are decomposed and reacted at a heated surface to form the thin film.

Chemical Vapor Deposition CVD => Chemical Vapor Deposition PE-CVD => Plasma Enhanced CVD MO-CVD => Metal Organic CVD Atmospheric pressure CVD (AP-CVD) Low-pressure CVD (LP-CVD) Ultrahigh vacuum CVD (UHV-CVD) Aerosol assisted CVD (AA-CVD) Direct liquid injection CVD (DLICVD)

Plasma Enhanced CVD Microwave plasma-assisted CVD (MP-CVD) Plasma-Enhanced CVD (PE-CVD) Plasma-Enhanced CVD Remote plasma-enhanced CVD (RPE-CVD)

Other Types of Chemical Vapor Deposition Atomic layer CVD (ALCVD)ALCVD Combustion Chemical Vapor Deposition (CCVD) Combustion Chemical Vapor Deposition Hot wire CVD (HWCVD) Metal organic chemical vapor deposition (MOCVD) Metal organic chemical vapor deposition Hybrid Physical-Chemical Vapor Deposition (HPCVD) Hybrid Physical-Chemical Vapor Deposition Rapid thermal CVD (RTCVD) Vapor phase epitaxy (VPE)

Applications of CVD

Horizontal APCVD Reactor CVD Reactors

Thermal CVD Reactor Chemical Vapor Deposition Apparatus

Chemical Vapor Deposition

CVD Growth Model The flow of reactants F is F  D G  -1

Plasma Enhanced (PE)CVD As the thermal budget gets more constrained while more layers are added for multi-layer metallization, we want to come down with the temperature for the oxide ( or other) CVD processes. One way for doing this is to supply the necessary energy for the chemical reaction by ionizing the gas, thus forming a plasma.

PVD Apparatus Physical Vapor Deposition Apparatus

PVD Film Properties Benefits Low substrate temperature Conformal film Relatively fast process Comparatively low cost Trade-offs Not stoichiometric film By-products incorporated Outgassing Cracking Peeling

CVD vs. PVD Chemical Vapor Deposition (CVD) relies on chemical reactions between reactants in the gas phase and/or on the substrate surface. Physical Vapor Deposition (PVD) is a thermal evaporation driven or energy driven process.

(PVD) Apparatus

Silicon CVD ‘Epitaxy’ When SiH 4 gas is used in a CVD reactor, a Si layer is deposited on the wafer surface. The size of the crystallites depends on the deposition temperature. At high enough temperature, the ad-atoms have enough kinetic energy to move on the surface and align themselves with the underlying Si. This is an epitaxial layer, and the process is called Epitaxy instead of CVD. At lower deposition temperatures, the layer is poly-crystalline Si (consisting of small crystallites)

The chemical reaction that produces the Si is fairly simple: SiCl 4(g) +2H 2(g) =( o C)=Si (s) +4HCl (g) Instead of SiCl 4 you may want to use SiH X Cl 4-X Silicon Epitaxy Process

CVD Used in Semiconductors LayerReaction equations Temperature (ºC) SiO 2 LTO TEOS HTO SiH 4 + O 2 -> SiO 2 + 2H 2 Si(OC 2 H 5 ) 4 -> SiO 2 + gas.RP SiCl 2 H 2 + N 2 O -> SiO 2 + 2N 2 + 2HCl SiH 4 + CO 2 H 2 -> SiO 2 + gas.RP Si 3 N 4 3SiH 2 Cl 2 + 4NH 3 -> Si 3 N 4 + 6HCl + 6H Polysilicon SiH 4 -> Si + 2H Tungsten selective blanket 2WF 6 + 3Si -> 2W + 3SiF 4 WF 6 + SiH 4 -> W + SiF 4 + 2HF + H

SiH 2 CI 2 + 2NO 2 = (900 °C) = SiO 2 + 2HCI + 2N 2 There are several possibilities, one is While this reaction was used until about 1985, a better reaction is offered by the "TEOS" process. Si(C 2 H 5 O) 4 = (720 °C) = SiO 2 + 2H 2 O + C 2 H 4. Si(C 2 H 5 O) 4 has the chemical name Tetraethylorthosilicate Silicon Oxide CVD Process

MO-CVD A technique for growing thin layers of compound semiconductors in which metal organic compounds, having the formula MR x, where M is a group III metal and R is an organic radical, are decomposed near the surface of a heated substrate wafer, in the presence of a hydride of a group V element. Abbreviated MOCVD.

Figure 1: Fabrication of (a) III–V-OI on Si substrate by DWB and (b) InGaAs-OI MOSFETs with metal S/D structure using Ni–InGaAs alloy. A first demonstration of a new metal source/drain technology for extremely thin body (ETB) indium gallium arsenide (InGaAs) transistor channels on insulator (OI) with silicon substrates has been reported by University of Tokyo, National Institute of Advanced Industrial Science and Technology and Sumitomo Chemical Co Ltd [SangHyeon Kim et al, Appl. Phys. Express, vol4, p114201, 2011].

MO-CVD: TMG + Arsine => GaAs The various techniques of growing epitaxial layers from the vapor phase can be divided roughly into two categories depending on whether the species are transported physically or chemically from the source to the substrate. In the physical transport techniques (Physical Vapor Deposition - PVD), the compound to be grown or its constituents are evaporated and subsequently transported through the relevant reactor toward the substrate. In the chemical transport techniques (Chemical Vapor Deposition - CVD), volatile species containing the constituent elements of the layer to be grown are produced first in- or outside the reactor and transported as streams of vapor towards the reaction zone near the substrate. These gaseous species subsequently undergo chemical reactions or dissociate thermally to form the reactants which participate in the growth of the film. The practical demand to decrease the growth temperature generated an intensive development trend of CVD processes based on metal organic compounds, decomposing at lower temperatures. This process is referred to as Metal Organic Chemical Vapor Deposition (MOCVD) or Organometallic Vapor Phase Epitaxy. The classical example is the growth of GaAs from Trimethylgallium (TMG) and Arsine (AsH 3 ). In our laboratory we apply this technique to grow GaN from TMG and Ammonia. However, this technique is based on a very precise control of the gas flow as can be estimated from the look into the gas mixing cabinet.

Planetary MOCVD reactor in an industrial setup (Photo courtesy of Aixtron)

Metal Organic Vapor Phase Epitaxy MO-VPE Metal organic vapor phase epitaxy (MOVPE), also known as organometallic vapor phase epitaxy (OMVPE) or metal organic chemical vapor deposition (MOCVD), is a chemical vapour deposition method of epitaxial growth of materials, especially compound semiconductors, from the surface reaction of organic compounds or metalorganics and metal hydrides containing the required chemical elements. For example, indium phosphide could be grown in a reactor on a substrate by introducing Trimethylindium ((CH 3 ) 3 In) and phosphine (PH 3 ). Formation of the epitaxial layer occurs by final pyrolysis of the constituent chemicals at the substrate surface. In contrast to molecular beam epitaxy (MBE) the growth of crystals is by chemical reaction and not physical deposition. organometallic chemical vapour deposition epitaxial growthcompound semiconductorsorganic compoundsmetalorganics chemical elements indium phosphide Trimethylindium phosphinepyrolysis molecular beam epitaxycrystals

MO-CVD Apparatus

PE-CVD Plasma-enhanced chemical vapor deposition (PECVD) is a process used to deposit thin films from a gas state (vapor) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creation of a plasma of the reacting gases. The plasma is generally created by RF (AC) frequency or DC discharge between two electrodes, the space between which is filled with the reacting gasesgasvapor solidsubstrateChemical reactionsplasma RFACDC electrodes

PE-CVD Apparatus Thermal - chemical vapor deposition A thermal-CVD system was built for carbon nanotubes production via gas phase or on substrate surface. The sketch of thermal-CVD system consists of quartz tube furnace which can operate till 1200 degree centigrade. The sketch of our equipment is shown in figure 1. Main advantages of a thermal-CVD are: the absolute ability for mass production of nanotubes material and the controllable growth of carbon nanotubes at a specific location on a substrate for incorporation in electronic device. Plasma Enhanced - chemical vapor deposition A controllable method for carbon nanotubes production is plasma enhanced-CVD. Such a system is often used to grow free standing vertically aligned MWCNT. The set-up which our laboratory is equipped with is a glow discharged type. Briefly, two electrodes are placed in a stainless-steel chamber. The grounded cathode plays the role of a substrate holder and Ohmic heater. On the anode is applied aprox.400V.

Low Pressure RF Plasma for PECVD of TiO2 on Plastics

Plasma Polymerization Plasma polymerization deposits molecules onto a surface as a conformal coating The molecules deposited are part of a network, often highly cross-linked Chemistry is tuned by the gas composition mixture, flow rate, and energy conditions A variety of very novel molecular networks can be formed in a straightforward manner

Plasma Deposition Plasma polymerization (or glow discharge polymerization) uses plasma sources to generate a gas discharge that provides energy to activate or fragment gaseous or liquid monomer, often containing a vinyl group, in order to initiate polymerization. Polymers formed from this technique are generally highly branched and highly cross-linked, and adhere to solid surfaces well. The biggest advantage to this process is that polymers can be directly attached to a desired surface while the chains are growing, which reduces steps necessary for other coating processes such as grafting. This is very useful for pinhole-free coatings of 100 picometers to 1 micrometer thickness with insoluble polymers.

Plasma Polymerization Schematic representation of bicyclic step-growth mechanism of plasma polymerization

Plasma Polymerization Hypothesized model of plasma-polymerized ethylene film (Wikipedia)

Plasma Polymerization Mechanism and Species Plasma contains many species such as ions, free radicals and electrons, so it is important to look at what contributes to the polymerization process most. The first suggested process by Westwood et al. was that of a cationic polymerization, since in a direct current system polymerization occurs mainly on the cathode. However, more investigation has led to the belief that the mechanism is more of a radical polymerization process, since radicals tend to be trapped in the films, and termination can be overcome by reinitiation of oligomers. Other kinetic studies also support this theory. In polymerization, both gas phase and surface reactions occur, but mechanism differs between high and low frequencies. At high frequencies it occurs in radical intermediates, whereas at low frequencies polymerization happens mainly on surfaces.cationic polymerizationradical polymerization

Summary CVD is a family of techniques –CVD, PVD, PE-CVD, MO-CVD Chemistry in the vapor phase –Surface reactions on the substrate Plasma can ‘enhance’ reaction conditions Used principally in semiconductor industry

References Microelectronics Processing Course - J. Salzman - Jan Microelectronics Processing Chemical Vapor Deposition Microelectronics Processing Course - J. Salzman – Fall Microelectronics Processing. Ion Implantation Wikipedia, CVD, PVD, PE-CVD, MO-CVD American Vacuum Society (AVS)