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These definitions are intended to give our users a start on these topics and not an exhaustive source.
More extensive sources are cited for our users benefit.

Wikipedia entries are used for general reference and should never be sited as real sources. We have only linked to the more complete entries.

Anisotropic
  • For processing purposes, it generally refers to an etch process that results in vertical sidewalls and features with higher aspect ratios.
  • Etches that follow the crystal planes are also referred to as isotropic etches.
  • Etches that result in these profiles are the result of preferential etching, either from crystallographic planes with different etch rates, or by protecting the sidewalls with a material that slow the etch as in Reactive Ion Etching
Broadband
Cassettes and Boats
  • Wafer boats are typically made of fused silica or silicon carbide and are intended for holding wafers during a high temperature process.
  • Wafer cassettes are typically made of metal, Teflon or plastic (polypropylene).
    • Wafers are stored and shipped in plastic cassettes.
    • Teflon cassettes are used for wet chemical processing due to their chemical resistance.
    • Metal and plastic cassettes are used to hold wafers in place for loading and unloading by a robotic wafer handling system.
Contamination Threat Materials
  • These are materials and substrates that represent a contamination threat to sensitive electronic structures - such as the standard MOS structure.
  • As such - these materials and substrates are subject to restrictions and can only be processed in certain tools.
  • Examples include
    • Gold or wafers with gold
      • Gold has a very high mobility at low temperatures and introduces deep bandgap traps that will reduce carrier lifetime
    • Copper or wafers with copper
      • Copper has a higher mobility than gold introduces deep bandgap traps that will reduce carrier lifetime
    • Potassium and Sodium
      • These are both light mobile ions that diffuse readily into silicon dioxide and introduce threshold voltage shifts in MOS structures.
      • Sources of Potassium in the lab outside of people are primarily wafers and equipment exposed to the KOH etch bath. Wafers receive an HCl decontamination treatment after KOH processing before they can move on.
      • Sources of sodium (Touching wafers) can come from certain photoresist developers. Wafers that have been exposed to Na based developers would need an HCl decontamination. This is why TMAH developers are also referred to as metal ion free developers as they are not NaOH based
    • III-V substrates
      • As the elements in compound semiconductors are dopants in silicon, these substrates are generally processed in separate equipment from silicon wafers.

(warning) Go here for further information on specific materials in the SMFL

Crucibles
  • Containers used to hold the evaporation material in an electron beam deposition system. The composition of the liner is matched to the material being deposited to minimize thermally created chemical interactions and maximize the thermal stability of the evaporation process.
Depth of Field (DOF)
  • In relation to a lithographic exposure process, it is the vertical height that the aerial image retains its information without degradation.
  • Example - Substrates with features coated with resist that are 2um in height and a DOF of 1um, the image will be not be in focus over the whole depth of your feature.
  • Increasing resolution by decreasing the wavelength and increasing the lens NA has the tradeoff of lowering the DOF
  • References
    • Moreau, Wayne. Semiconductor Lithography. Plenum Press, 1991.
Diffusion
  • Diffusion is the movement of a substance from an area of high concentration to an area of lower concentration. In semiconductor processing it refers to the movement of dopant atoms within the semiconductor. Diffusion is temperature dependent.
  • References
Dopant
  • A dopant is an element added in small quantities to a semiconductor to change its electrical properties.
  • Dopants are introduced into a semiconductor by diffusion or ion implantation. In the diffusion method, a high concentration of dopant atoms is introduced onto the surface of the semiconductor. A high temperature step allows the dopants to diffuse in. In the ion implant method, ionized dopant atoms are accelerated to a high energy, directed to the surface of the semiconductor and allowed to collide and penetrate into the crystal. A high temperature treatment follows an ion implant step to allow activation of the dopants.
  • References
Dry Etching

A process by which a plasma is used in an evacuated chamber (with specific introduced gases) to generate chemically active species and/or energetic ions with the intent of removing a film on a substrate. There are generally three types of dry etching processes.

Physical/Sputter Etch
  • Energetic Ions bombard the surface to physically remove the film on the substrate (akin to sandblasting)
  • Not selective - will remove masking layers as well as film to be etched.
  • Low process pressures
  • Can be highly anisotropic
  • The PE440 Sputter System uses a sputter etch to clean the surface of the substrate before depositing metals - useful when depositing multiple layers or for cleaning contacts before depositing contact metal.
Reactive Ion Etch
  • Combination of chemical etch and energetic ions etching
  • More selective - will remove masking layers as well as film to be etched.
  • Anisotropic
Plasma Etch
  • Chemically active species are generated
  • Can be very selective.
  • Higher process pressures
  • Isotropic
Evaporation
  • Describes a physical vapor deposition (PVD) technique whereby materials under vacuum are heated. As they are heated, their vapor pressure increase until the point where the material evaporates out of the source an onto the surrounding substrates.
  • The heating of the material can be accomplished by thermal (electrical resistance) methods or by focusing a beam of electrons onto the source material.
Evaporation Sources
  • These are made from tungsten or molybdenum wire or foil. Their purpose is to hold the evaporant material in place for heating, melting and evaporation. The tungsten and moly materials retain their strength even at the high temperatures required for evaporation.
  • There is a large variety of shapes, sizes for different materials and applications.
Ellipsometry
  • Ellipsometry measurement methods employ the analysis of the change in polarized light reflected off of a surface.
  • Multi-spectral & multi-angular techniques add the the range of films that can be modeled and measured.
Hardbake

A lithographic process step in which the developed, patterned photoresist is subjected to a elevated temperature in either an oven or a vacuum hotplate. This heat treatment serves to drive out any remaining solvent, help with adhesion and subsequent etch resistance.

  • References
    • Wolf, S. Microchip Manufacturing. Lattice Press, 2004.
    • Rai-Choudhury, P. ed. Microlithography, Micromachining, and Microfabrication - Vol 1. SPIE. 1997.
    • Sheats, James R. and Smith, Bruce W. Microlithography. Marcel Dekker, Inc, 1998.
    • Moreau, Wayne. Semiconductor Lithography. Plenum Press, 1991.
g-line
  • An emission line of the mercury discharge lamp centered about 436nm.
  • In the visible portion of the EM spectrum.
    • First generation of lithography tools used this emission line for photoresist exposure.
  • Yields resolution of 1um in resist. See Description of Rayleigh equation for discussion on resolution dependence on wavelength.
i-line
  • An emission line of the [mercury discharge lamp centered about 365nm.
  • Second generation of lithography tools used this emission line for photoresist exposure.
  • In the ultraviolet portion of the EM spectrum.
  • Yields resolution of 0.5um in resist. See Description of Rayleigh equation for discussion on resolution dependence on wavelength.
Ion Implant
  • Ion implantation is a semiconductor doping process in which ions of a material are extracted, accelerated to a particular energy level and then steered towards a substrate. The ion of interest strikes the surface of the substrate with enough energy to implant itself in the substrate. The depth of the implant depends on the species and the implant energy. The implanted ions can cause considerable damage to the crystal structure of the substrate which is generally annealed out in subsequent processing
Isotropic
  • For processing purposes, it generally refers to an etch process that results etches equally in all directions.
  • Acts to widen defined features through undercutting. Can be used for advantage as in liftoff processes
Liftoff
  • A lithographic technique where a material (usually metal) is deposited over a patterned photoresist. The photoresist is then dissolved which in turn lifts off the material that was deposited on top of the dissolved photoresist. The material that was deposited in the photoresist openings is all that remains.
  • Liftoff is particularly useful when a material is difficult to etch by other means.
  • The starting layer of photoresist should be thicker than the metal being deposited to ensure a discontinuous layer of metal. Liftoff works best when the photoresist layer is wider at the top than the bottom. After the metal is deposited, a small gap remains and allows the photoresist to easily dissolve in the solvent.
  • Details on the liftoff process used in the SMFL
Loadlocked
  • Loadlocked refers to a system where wafers are loaded into an intermediate chamber before being loaded into a process chamber.
  • The loadlocked chamber is cycled between atmospheric pressure and vacuum as wafers are loaded and unloaded.
  • The main process chamber is only opened when the loadlocked chamber is under vacuum. This ensures that the process chamber never reaches atmospheric pressure, helps prevent moisture and contamination from entering the process and provides a more controllable process.
LPCVD
  • Acronym for Low Pressure Chemical Vapor Deposition
  • Used for depositing thim films on substrates.
  • Gases are fed into a vacuum system where they are reacted to form a thin film on a substrate
  • Thermal energy is used to drive the reaction as opposed to plasma as in PECVD
  • The SMFL ASM Tubes are capable of depositing poly-Si, nitride, and oxide using LPCVD.
Mercury Arc Lamp
  • The mercury arc lamp is the basic tool for generating the ultra-violet radiation used in the exposure of many photoresists.
  • The most commonly used spectral output is the i-line centered at 365nm. This wavelength is good for exposures down to 0.5 um linewidths.
    • The g-line output (436nm) was used at the start of the semiconductor industry.
    • When the range of UV output is used (365 to 436nm), this is commonly referred to as broadband exposure.
Nomarski Imaging
Oxidation
  • The process where silicon combines with oxygen to form an insulating layer. The resulting oxide is used in the fabrication of many semiconductor devices.
  • Oxidation is temperature dependent. Oxidation rates are also affected by water vapor and the presence of chlorine.
  • References
Photomask
  • This is the master that is used to transfer the pattern information to the photoresist coated substrate.
  • Generally made from fused quartz (for deep UV applications, dimensional stability), or from soda lime glass.
  • Mask blank is generally coated with chrome that is patterned with the design that is desired to print on the wafer/substrate. The top surface of the chrome is treated with an anti-reflection layer to prevent standing waves and reflections between the two plate surfaces.
  • The SMFL can write 4", 5", 6", and 7" square photomasks in our MEBESIII mask writing system
  • References
    • Rai-Choudhury, P. ed. Microlithography, Micromachining, and Microfabrication - Vol 1. SPIE. 1997.
    • Enyon, Benjamin G. & Wu, Banqiu. Photomask Fabrication Technology. McGraw-Hill, 2005.
    • Wikipedia Photomask Entry
Photomask Materials
Photoresist
  • A polymer with a photoactive component that is sensitive to UV radiation. Can either be positive or negative acting depending on whether or not the resist becomes more soluble with exposure to ultra-violet radiation (positive) or less soluble(negative) in the subsequent developer.
  • References
    • Rai-Choudhury, P. ed. Microlithography, Micromachining, and Microfabrication - Vol 1. SPIE. 1997.
    • Sheats, James R. and Smith, Bruce W. Microlithography. Marcel Dekker, Inc, 1998.
    • Moreau, Wayne. Semiconductor Lithography. Plenum Press, 1991.
    • Wikipedia Photoresist entry
PECVD
  • Acronym for Plasma Enhanced Chemical Vapor Deposition
  • Gases are fed into a vacuum system where they are combined/reacted to form a film on the substrates.
  • Plasma is used as the energy source to form the film reactants rather than heat as in LPCVD
  • Films can be deposited at lower temperatures, often the energy and frequency of the plasma can be used to adjust the film properties.
  • The SMFL P5000 has two PECVD chambers for deposition of oxides, nitrides and a-Si.
Piranha Clean

This refers to a mixture of sulfuric acid and hydrogen peroxide. It is mixed in a volume ratios of 1-4:1 are used at temperatures of 100°C and higher. The mixture is often referred to as Piranha etch because of its aggressive ability to remove organics.

  • References
    • Kern, W. ed. Handbook of Semiconductor Wafer Cleaning Technology. Noyes Publications, New Jersey, 1993.
    • Wikipedia entry on Piranha
Pyrophoric

This refers to a material that will spontaneously ignite upon exposure to air. Silane is one example of a pyrophoric material.

Rapid Thermal Annealing
  • Also known as RTP
  • The fast heating of substrates up to high temperatures of ~1200C.
  • Used for annealing implant damage, dopant activation, thermal oxidation, silicide formation.
RCA Clean

This refers to a particular multiple step cleaning process developed by Werner Kern in 1965 at the Radio corporation of America (RCA). It is intended to remove light organic contamination, light mobile ions, and heavier metal ions that represent a contamination threat to integrated circuits. It also includes a hydrofluoric (HF) acid dip to remove the oxide that is chemically grown by the hydrogen peroxide. It is generally used before thermal oxidation, CVD and diffusion processes.

  • The first step is usually a sulfuric acid / hydrogen peroxide (Piranha Clean) to remove light organics
  • Next is the SC1 Clean or APM (Ammonia/peroxide mix). This is a mixture of Ammonium Hydroxide / Hydrogen Peroxide and water.
  • The last step is the SC2 Clean or HPM (Hydrochloric/peroxide mix). This is a mixture of Hydrochloric acid / Hydrogen Peroxide and water.
Softbake

A lithographic process step in which substrates are subjected to an elevated temperature after they have been coated with photoresist This is typically done in either an oven or a vacuum hotplate. This heat treatment serves to drive out most of the casting solvent. Presence of the casting solvent during the subsequent development can lead to poor adhesion and resist loss. Softbake temperatures that are too high can lead to degradation of the photoactive (PAC) compound in the the photoresist

  • References
  • *Wolf, S. Microchip Manufacturing. Lattice Press, 2004.
    • Rai-Choudhury, P. ed. Microlithography, Micromachining, and Microfabrication - Vol 1. SPIE. 1997.
    • Sheats, James R. and Smith, Bruce W. Microlithography. Marcel Dekker, Inc, 1998.
    • Moreau, Wayne. Semiconductor Lithography. Plenum Press, 1991.
Spectrophotometry
  • Spectrophotometry is used as a measurment technique for thin, optically transparent films
  • It is based on the measurement of the reflected interference from films of known refractive indexes.
  • It is useful for the measurement of oxides, nitrides, photoresist.
Sputter Deposition

Sputtering is the term used to describe a physical vapor deposition technique where energetic ions are generated in a plasma (DC, RF) and then accelerated towards the target / deposition material. Once the ions strike the target, they transfer their energy and eject the target material from the surface. The ejected target material is deposited on the nearby substrates.

  • The plasma can be generated through DC or RF (Radio Frequency) means.
    • DC is typically used to deposit conducting materials
    • RF plasmas are used to deposit either conductive or non-conductive materials.
  • The characteristics (deposition rate, grain size, stress, etc.) of the deposited film is highly dependent on the type of plasma, power, pressure, etc. Depositing 1um in one system and 1um in a different system will most likely give you two different films.
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