College of Engineering / Alabama Microelectronics Science and Technology Center / Capabilities


Patterning (to define micro/nano features on a sample)

Optical Lithography – A method to pattern a photosensitive material (known as photoresist) on the surface of a sample for transfer of a mask pattern. Light is passed through the mask and interacts with the photoresist, which is subsequently developed to reveal the transferred pattern. This is a fast, large area patterning method.

Electron Beam Lithography – Also known as e-beam lithography. A direct patterning method where an electron beam is scanned across a sample and used to write the pattern directly into an e-beam resist on the sample. This is a very high resolution, but quite slow patterning method.

Printing – Similar to an office “ink jet” printer, inks that incorporate the desired target materials to be deposited can be used to print features directly onto a sample.

Direct Write Laser – Also known as DWL. A laser is used to directly write the pattern into a photoresist that is sensitive to the wavelength of the laser. With use of a femtosecond laser, this method can also be used to directly ablate (remove) regions of thin-film materials that were previously deposited, leaving behind the desired pattern.

Lift-Off – In this process, a thin layer of a desired material is deposited as a blanket on top of resist that was previously patterned using one of the patterning methods described above. The thin layer is usually thinner than the resist material. The resist material under regions of the thin-film material is then dissolved using a wet dissolution process and removed, thereby lifting-off the thin-film material in those regions and leaving behind the thin-film material in the regions that were not lifted-off.

Deposition (to deposit thin films on a sample)

Evaporation – A physical deposition method performed in a high vacuum, in which a target material is vaporized by heating and subsequently condensed onto the surface of a cooler sample. The target material can be heated using a resistive heater or by use of an electron beam.

Sputtering – A physical deposition method performed in a high vacuum, in which a target material is removed from the surface of a target by use of ion bombardment using inert ions. The “cloud” of target materials then deposits onto the surface of a nearby sample.

Plasma Enhanced Chemical Vapor Deposition – Also known as PECVD. A chemical vapor deposition method, performed in a vacuum chamber, in which precursor gases are broken down (“cracked”) using a plasma, and the desired chemical species reacts chemically while depositing onto the surface of a sample. The use of the plasma allows processes that are generally below 400 C.

Atomic Layer Deposition – Also known as ALD, or, for plasma enhanced methods, PEALD. A self-limiting, atomic monolayer-by-monolayer deposition method performed in a vacuum at elevated temperatures that can produce very well controlled, conformal, high quality films.

Electroplating – A physical deposition method in which a desired material is driven out of a solution onto a targeted sample surface using an electrical current. (Electroless plating method also exist that do not require current flow.)


Etching (to remove specific regions of films on a sample)

Wet Etching – A sample with a patterned resist is subjected to a chemical etch solution to remove the exposed material that is not protected by the resist. Generally viewed as a quick etching method that can provide reasonable feature resolution. The etch is usually isotropic, but some wet etches can be directional or anisotropic.

Dry Etching – Also known as gaseous or plasma etching. A method that is similar to wet etching but that uses a gas as the chemical etchant. This can provide higher feature resolution and better control than wet etching.

Reactive Ion Etching – Also known as RIE or DRIE (for deep reactive ion etching). A high resolution, directional (anisotropic) etch process that uses a reactive chemical species in combination with directionally-driven ions to produce very fine and very high aspect ratio features.

Lapping and Polishing – A method to thin and/or polish the surface of a substrate through the use of a very flat polishing disk and a mechanically abrasive slurry.

Chemical Mechanical Polishing – Also known as chemical mechanical planarization or CMP. A method that uses both chemical and mechanical processes, through the use of chemical additives to the lapping and polishing process. The introduction of the chemical process provides control over polish rate and can allow enhanced selectivity between which materials are removed.


Thermal Processing (to modify the properties of materials on a sample)

Oxidation – Process of forming a thin, precise, controlled-thickness oxidized layer on the surface of a sample by heating it to a high temperature in the presence of oxygen within an oxidation furnace. Time and temperature are used to control the thickness and quality of the formed oxide layer.

Annealing – Process used to alter the properties (electrical, mechanical, thermal) of a sample by heating to a specified temperature or following a specific temperature profile.

Rapid Thermal Annealing – A method of performing annealing that targets annealing of the surface of a sample while the bulk or layers under the surface layer are minimally changed or unchanged.

Diffusion – A thermally-driven process that causes dopant atoms to diffuse within the sample to form the desired dopant profile and become electrically activated. The dopants can be introduced using doping (see doping description below).



Wet Clean – Solution-based methods to remove films or contaminants from a sample (front and back) through etching, dissolving, or rinsing. Samples can be soaked, sprayed, or stirred and the use of sonication can assist in the process.

Dry Clean – Also known as plasma cleaning, or plasma ashing, in which a gaseous plasma species (for example oxygen or fluorine) is reacted with contaminants on the sample surface to convert the contaminant into either volatile compounds that release from the sample surface or other compounds that can be removed using a subsequent wet clean process.


Metrology and Characterization (to determine physical, mechanical, electrical, etc. properties of structures on a sample)

Profilometry – Methods to map or profile the surface topology of a sample. These systems can use a scanned mechanical stylus, optical reflection/interference or atomic force.

Optical Microscopy – Use of an optical microscope to investigate microscopic samples using an optical system that provides much higher resolution than an unaided eye.

Ellipsometry – High resolution method for determining film thicknesses and optical properties (constants).

Scanning Electron Microscopy – Also known as SEM. A microscopy method that uses an electron beam that is scanned across the surface of a sample providing extremely high resolution images of the surface morphology. SEM systems with suitable options can also provide other information about the sample, such as identification of the chemical species.

Atomic Force Microscopy – Also known as AFM. A microscopy method that uses a very fine tip that is scanned across the surface of a sample. AFM can provide very high resolution images and can be performed in multiple modes depending on the desired data to be gathered.

Electrical Characterization – This encompasses many types of characterization using electrical (current-voltage, capacitance, resistance, etc.) techniques that can be performed on wafers, individual die, etc. in a desired environment that can include ambient laboratory environment, within a cryogenic probe station, packaged and inserted into other test chambers, etc. These methods can be performed on bulk materials, thin films, patterned structures, individual devices and circuits.


Packaging (to allow connectivity to and protect fabricated samples)

Dicing – Cutting a substrate or wafer into smaller pieces (also known as ‘die’) using a high precision dicing saw or laser.

Wire Bonding – A method to form electrical connections using tiny wires that are bonded from wire bond pads on the sample to desired connection sites within a package or on a printed circuit board (PCB), printed wire board (PWB), multi-chip module (MCM) or other suitable substrate.

Flip-Chip Bonding – A method of attaching a die (chip) to a board or substrate in which a chip (with electrical interconnect bumps) is flipped upside down, aligned to and then attached to an underlying substrate thereby making electrical interconnections between the chip substrate.

Vacuum Package Sealing – A process to seal or attach a lid to an electrical package (for example using solder reflow) for a sample within the package. This is generally performed inside a high vacuum. This process can also be performed using an inert gas that is back-filled into the packaging chamber such that the sealed package will have an inert ambient gas environment inside the package.

Decapsulation – A process to remove the protective cover or dissolve the plastic package containing a packaged die in order to harvest said die for use in other packaged systems such as a multi-chip module (or MCM).



Doping – Process in which a chemical species (dopant) is introduced into an underlying film through directly implanting (using an ion implanter) or through thermal diffusion from a deposited doping layer. This process can be very precisely controlled and is used to control the electrical properties of the targeted doped layer.