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Week 1: MEMS and cleanroom introduction

Case study: thermo-mechanical micro-actuator

^|^{While there are several options that can be used to etch silicon,}^|^{such as dry plasma silicon etching.}^|

Week 2: Chemical vapor deposition (CVD)

CVD techniques at different operating pressure, plasma-enhanced CVD and metal-organic CVD

^|^{The light is caused mostly by accelerating free electrons,}^|^{but all molecules in the plasma become agitated}^|^{Schematically, one can imagine that without plasma}^|^{to be converted to a metal atom in this example.}^|^{If now the RF plasma is switched on,}^|

Specific CVD processes for silicon-based materials and diamond

^|^{A microwave generator creates the energy}^|^{for generation of the plasma in the reactor.}^|^{A typical microwave plasma CVD growth rate for diamond}^|

Week 3: Physical vapor deposition (PVD)

Sputtering: introduction and plasma formation

^|^{In fact many more than for thermal evaporation.}^|^{I will first show some basic physical principles on how a plasma is created}^|^{for our purposes, show the different plasma zones}^|^{values in the order of a couple of hundred mTorrs.}^|^{A plasma is then created by applying a high voltage}^|^{Let's have a short look at what}^|^{plasma is and how it works for our purpose here.}^|^{It is commonly also referred to as the fourth state of matter.}^|^{By the way, plasma is also used for dry etching processes}^|^{cover in detail in his corresponding lesson.}^|^{The simplest form of plasma for our purpose, the DC plasma,}^|^{It is not used for microfabrication applications}^|^{as plasma in this regime is neither energetic nor stable.}^|^{are ejected and sustain the plasma.}^|^{Without these electrons, the plasma would rapidly vanish.}^|^{Finally, the plasma reaches a steady state}^|^{to a lower energy level.}^|^{The plasma is luminous, and this regime is called "glow discharge".}^|^{In this regime, the plasma is stable and energetic enough}^|^{In this photograph, you can see the glow of the plasma}^|

Sputtering: spatial zones and Paschen law

^|^{Consequently, the electric field is not constant along the plasma}^|^{and dark areas, as shown here in this slide on the upper right side.}^|^{And we have the plasma chamber with the cathode and the anode}^|^{and different zones in the plasma due to the different mobility}^|^{of ions and electrons.}^|^{For more details about plasma zones, please have a look}^|^{This is showing a chamber with the cathode and the anode}^|^{and the plasma in between.}^|^{is placed in the negative glow.}^|^{Therefore, the plasma column can be simplified from here to here}^|^{The potential changes very abruptly close to the electrodes}^|^{in the plasma sheets and it is constant in the glow region of the plasma.}^|^{There is a very steep slope of the potential difference}^|^{of the cathode into the plasma vacuum,}^|^{and here again a steep slope, and we approach the anode.}^|^{And these are the two plasma sheets.}^|^{The origin of this plasma sheet, as well as the computation}^|^{Here we have the typical curve, for example a gas like argon.}^|^{And we plot the breakdown voltage and the plasma is breaking down}^|^{behind sputtering, about how to create a plasma}^|

Sputtering: DC, RF, magnetron

^|^{However, it suffers from two main limitations.}^|^{Firstly, the plasma is present in}^|^{due to the accumulation of positive Argon ions on the target.}^|^{As a result, the plasma would stop.}^|^{RF sputtering main difference with DC sputtering is the way}^|^{how the plasma is created.}^|^{and the substrate is placed on the anode.}^|^{The difference is that, here the plasma is created applying}^|^{which requires very efficient cooling of the target during the sputtering.}^|^{In addition, as for the DC sputtering, the plasma is not localized}^|^{thus substrate cooling is also required.}^|^{To even further increase the plasma efficiency}^|^{here, magnetic field, that are going into the plasma}^|^{deposition of film with higher purity.}^|^{In addition, the plasma is localized.}^|

Sputtering: ion target interactions

^|^{Indeed, when all the walls of the chamber are grounded,}^|^{a plasma will still install between the two electrodes, as wanted,}^|^{of the cathode, a grounded shield is placed at a distance}^|^{less than that of the plasma sheath}^|^{This way, the space between the shield and the cathode is too small}^|^{to allow plasma formation and the plasma is contained in front of the target.}^|

Sputtering: film growth and control parameters

^|^{changing either the pressure or the inter-electrode distance}^|^{will alter the plasma stability.}^|^{There is also a risk of contamination of the deposited thin film}^|^{by argon atoms from the plasma if the pressure is too high.}^|^{Reversing the electrode's polarity and creating a low energetic plasma}^|^{and break oxide and surface bonds to activate the surface.}^|^{Such dry cleaning process using a plasma is less efficient than wet cleaning}^|

Sputtering: examples

^|^{in oxygen plasma}^|

SUPPLEMENTARY Other techniques: ion plating, MBE, PLD, …

^|^{In the case of IAD,}^|^{a plasma is created}^|^{between the keeper and the hollow cathode,}^|^{creating a plasma within the hollow cathode.}^|^{Shown here.}^|^{Once the plasma is stable in the hollow cathode,}^|^{Both come from the fact}^|^{that no plasma is used}^|^{can be better controlled.}^|^{As there is no plasma close to the substrate.}^|^{by the target}^|^{a plasma plume is created}^|^{because of surface boiling or shockwaves}^|^{due to the plasma plume expansion.}^|^{the heat diffusion and melting is reduced}^|^{and the material is forced directly into plasma state}^|

Week 5: Dry etching (DE)

Dry etching in a gas plasma; etching anisotropy

^|^{in a gas plasma.}^|^{A plasma is defined}^|^{However, this gas becomes reactive}^|^{when it is brought to the plasma state.}^|^{The plasma can be created by applying}^|^{A CF4 oxygen plasma}^|^{to vary the conditions of the plasma}^|

Deep dry etching of silicon; dry etching without a plasma

^|^{that use intrinsic reactive gases}^|^{and that do not require to have the gas in the plasma state,}^|^{Xenon fluoride gas etching of silicon without development of a plasma}^|^{This process requires much simpler equipment}^|^{than a plasma etcher.}^|^{Another example of gas phase etching without a plasma}^|^{which indeed is orders of magnitude less complex and much cheaper}^|^{than a plasma reactor.}^|^{in which the etching gas and the polymerization gas}^|^{are simultaneously introduced in the plasma reactor,}^|

Theoretical concepts of plasma generation

^|^{In this lesson, we will introduce some theoretical concepts}^|^{that characterize a plasma in dry etching equipment.}^|^{A plasma is a collection of excited neutral molecules,}^|^{Such a layer close to an electrode is therefore called an ion sheath.}^|^{As a plasma is a special electrically conducting medium,}^|^{is reduced or absent.}^|^{A plasma is defined as an ionized gas,}^|^{of electrons and of ions.}^|^{A plasma is usually generated starting from a gas of pressures}^|^{of 10^-3 to 1 millibar.}^|^{The degree of ionization in a plasma is rather low,}^|^{or one of 10,000 molecules is ionized.}^|^{This means, also, that the majority of molecules in the plasma are neutral.}^|^{that are accelerated in the electric field.}^|^{The presence of a plasma is revealed}^|^{Due to the low gas temperature,}^|^{a glow discharge plasma is therefore called a cold plasma.}^|^{A typical frequency that is used for the generation of a plasma}^|^{because it's connected to earth.}^|^{The average voltage within the plasma itself}^|^{as some electrons from the plasma}^|^{over which current transport}^|^{from the plasma to the electrode}^|^{is however, that the plasma}^|

Types of dry etching equipment and plasma sources

^|^{In this lesson, we will present main dry etching equipment.}^|^{Also we will introduce some of the plasma sources}^|^{It is one of the first etching reactors used in semiconductor microfabrication.}^|^{It exploits a chemical oxygen plasma to remove polymers}^|^{Besides the use of oxygen for removal of organic layers,}^|^{one can also use a CF4 plasma in this reactor}^|^{chemical downstream reactor.}^|^{A microwave plasma is generated remotely from the etching chamber}^|^{Also, aluminium or aluminium oxide is used for this transfer tube}^|^{to reduce chemical interactions with the plasma during transfer.}^|^{in strong ion bombardment, even on insulating surfaces on the wafer.}^|^{The electrical impedance of a capacitive plasma source}^|^{to couple the impedance of this plasma}^|^{and thus sputter materials can eventually diffuse into the plasma}^|^{we mention here the etching of gallium arsenide.}^|^{We need here a chlorine plasma at a considerable pressure}^|^{to avoid damage of the material by the ion bombardment.}^|^{However, this obliges to have very low plasma density}^|^{a different electrode geometry than a diode}^|^{to decouple plasma generation from the generation}^|^{of the negative substrate voltage bias.}^|^{Such decoupling of the plasma generation from the generation of the bias}^|^{were significantly increased, typically by an order of magnitude.}^|^{As examples of these new plasma sources, we will explain now briefly,}^|^{the so called inductively coupled plasma source or ICP source,}^|^{operated at 13.5 megahertz}^|^{is separated from the plasma by a dielectric wall}^|^{within the skin depth of the plasma, which is a few centimeters.}^|^{The plasma acts like a kind of secondary transformer}^|^{For an ICP reactor, a high voltage on the lower electrode}^|^{is not required, so the plasma potential can be low.}^|^{Still, the plasma density can be high,}^|^{in the sheet, compared to a diode source.}^|^{The plasma operates well at low pressures of 10^-3 to 0.1 millibar.}^|^{of variable series and shunt capacitors that are adjusted here.}^|^{This type of plasma has a small capacitive coupling compared}^|^{to the plasma generated in a diode reactor,}^|^{because the coil is separated from the plasma}^|^{by a rather thick, dielectric wall.}^|^{However, the plasma needs to be initiated in the beginning via capacitive coupling.}^|^{We are here in the cleanroom and show the outside of an ICP reactor.}^|^{Inside of the plasma source is a coil}^|^{during maintenance of the ICP etching system.}^|^{Another type of new plasma source is the electron cyclotron resonance}^|^{is carried by a wave guide and coupled to the plasma}^|^{around which electrons can circulate.}^|^{The plasma absorbs power at a location}^|^{with the rotating electrical field of the ECR wave.}^|^{Finally, we mentioned as one of the new plasma sources, the helicon source,}^|^{also in presence of a magnetic field.}^|^{to that of ICP and ECR sources.}^|^{This slide summarizes the plasma densities that are obtained}^|^{with the various plasma sources as indicated here,}^|^{What we see on this slide is that going through more modern equipment,}^|^{we go to lower working pressures and higher plasma densities.}^|^{and the flux of the reactive species towards the wafer.}^|^{We then introduced three of the newer plasma sources}^|^{from the reactive species flux.}^|^{These were the inductively coupled plasma source,}^|

Ion beam etching

^|^{are not possible.}^|^{An advantage of an ion beam source over a plasma reactor}^|^{as the number of species and possible chemical reactions are limited,}^|^{contrary to what happens in a plasma reactor.}^|

Examples of etching processes for Si-based materials

^|^{and one obtains here a selectivity towards silica etching of 5:1}^|^{for the conditions of the plasma used.}^|^{in combination with a halocarbon plasma}^|^{it can be charged by the ions from the plasma}^|

Examples of etching processes for organic films and metals

^|^{One typically uses an oxygen plasma}^|^{The silicon dioxide was deposited}^|^{using a plasma enhanced}^|^{can be reduced}^|^{when one uses a plasma at the lower pressure,}^|^{because one has used a chlorocarbon plasma}^|^{one would have used a silicon dioxide mask,}^|^{and a plasma gas that did not contain carbon,}^|^{Also, one can apply}^|^{a plasma etching step in oxygen}^|^{We have used here a low pressure argon chlorine mixed plasma}^|^{or a fluorine plasma}^|

Week 6: Wet etching (WE)

HF bath for SiO2 and glass wet etching

^|^{after which an oxygen plasma}^|

Anisotropic wet etching of silicon in alkaline baths

^|^{While there are several options that can be used to underetch,}^|^{such as dry plasma etching, and isotropic silicon etching,}^|

Week 4: Lithography

Week 1: MEMS and cleanroom introduction

Week 1: MEMS and cleanroom introduction

Week 3: Physical vapor deposition (PVD)

Week 4: Lithography

Week 5: Dry etching (DE)

Week 6: Wet etching (WE)

Week 2: Chemical vapor deposition (CVD)

Week 4: Lithography

Week 7: Inspection and Metrology

Week 2: Chemical vapor deposition (CVD)

Week 1: MEMS and cleanroom introduction

Week 4: Lithography

Week 5: Dry etching (DE)

Week 6: Wet etching (WE)

Week 5: Dry etching (DE)

Week 6: Wet etching (WE)

Week 1: MEMS and cleanroom introduction

Week 1: MEMS and cleanroom introduction

Week 1: MEMS and cleanroom introduction

Week 7: Inspection and Metrology

Week 2: Chemical vapor deposition (CVD)

Week 5: Dry etching (DE)

Week 7: Inspection and Metrology

Week 7: Inspection and Metrology

Week 1: MEMS and cleanroom introduction

Week 3: Physical vapor deposition (PVD)

Week 6: Wet etching (WE)

Week 2: Chemical vapor deposition (CVD)

Week 3: Physical vapor deposition (PVD)

Week 4: Lithography

Week 5: Dry etching (DE)

Week 6: Wet etching (WE)

Week 7: Inspection and Metrology

Week 2: Chemical vapor deposition (CVD)

Week 3: Physical vapor deposition (PVD)

Week 4: Lithography

Week 1: MEMS and cleanroom introduction

Week 1: MEMS and cleanroom introduction

Week 3: Physical vapor deposition (PVD)

Week 4: Lithography

Week 6: Wet etching (WE)

Week 7: Inspection and Metrology

Week 1: MEMS and cleanroom introduction

Week 3: Physical vapor deposition (PVD)

Week 4: Lithography

Week 7: Inspection and Metrology

Week 1: MEMS and cleanroom introduction

Week 3: Physical vapor deposition (PVD)

Week 4: Lithography

Week 7: Inspection and Metrology

Week 5: Dry etching (DE)

Week 7: Inspection and Metrology

Week 1: MEMS and cleanroom introduction

Week 7: Inspection and Metrology

Week 1: MEMS and cleanroom introduction

Week 4: Lithography

Week 7: Inspection and Metrology

Week 4: Lithography

Week 7: Inspection and Metrology

Week 7: Inspection and Metrology

Week 1: MEMS and cleanroom introduction

Week 2: Chemical vapor deposition (CVD)

Week 3: Physical vapor deposition (PVD)

Week 4: Lithography

Week 5: Dry etching (DE)

Week 6: Wet etching (WE)

Week 3: Physical vapor deposition (PVD)

Week 5: Dry etching (DE)

Week 4: Lithography

Week 4: Lithography

Week 6: Wet etching (WE)

Week 7: Inspection and Metrology

Week 1: MEMS and cleanroom introduction

Week 5: Dry etching (DE)

Week 6: Wet etching (WE)

Week 3: Physical vapor deposition (PVD)

Week 6: Wet etching (WE)

Week 3: Physical vapor deposition (PVD)

Week 4: Lithography