Thin films

The NanoFab offers a wide variety of thin film deposition techniques. These techniques include plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD) and physical vapor deposition (PVD).

Atomic layer deposition

The ALD film growth technique utilizes self-limiting surface chemistry along with the appropriate source gases to generate monolayer films. The growth process works by exposing the substrate to alternating, sequential pulses of precursor gases, separated by inert gas purges, building films layer by layer to control thickness at the atomic scale. 

These monolayers are very conformal, from 50:1 to as high as 2500:1 aspect ratio. Thus, ALD films provide excellent step coverage over features. The process sequences are computer controlled to enable repeated steps and the fabrication of thicker layers. One example is the use of trimethylaluminum (TMA) plus water vapor to grow aluminum oxide (Al2O3). Its use in the semiconductor industry has advanced ALD rapidly in recent years to develop thin, high-K gate dielectric layers.

NanoFab ALD tool

Tool	Film	Precursors	Temp	Size
Cambridge Savannah S100 ALD	Al2O3  HfO2    TiO2	Trimethylaluminum, Tetrakis(dimethylamido)hafnium, Tetrakis(dimethylamino)titanium	180C	Up to 4” wafer

Plasma enhanced chemical vapor deposition (PECVD)

Plasma enhanced chemical vapor deposition is a process achieved by introducing reactant gases between parallel electrodes — a grounded electrode and an RF-energized electrode. The capacitive coupling between the electrodes excites the reactant gases into a plasma, which induces a chemical reaction and results in the reaction product being deposited on the substrate. The substrate, which is placed on the grounded electrode, is typically heated to 350C with processing pressures near 1.0 Torr. 

PECVD reactors usually deposit dielectrics, such as silicon dioxide or silicon nitride, and provide very good step coverage. The deposition processes can be run at lower temperatures though resulting in lower quality films. Our PECVD films include silicon dioxides (SiO2), silicon nitride (Si3N4) and silicon oxynitride (SiON) films.

NanoFab PECVD tool

Tool	Film	Process gases	Temp	Size
Oxford PECVD System 100	SiO2, Si3N4, SiON	5%SiH4/N2, N2O, NH3, N2	350C is typical for quality films	3,4,5,6 & 8” wafers

Physical vapor deposition

PVD deposition techniques include sputtering and evaporation. Sputtering provides good step coverage over topographical features. Evaporation results in a line-of-sight deposition and is the preferred deposition technique when patterning by the lift-off method.

Sputtering is a plasma-based deposition process in which energetic ions are accelerated towards a target. The ions strike the material target, and atoms are ejected (or sputtered) from the surface. These atoms travel towards the substrate and incorporate into the growing film. Magnetron sputtering is a deposition technology involving a gaseous plasma which is generated and confined to a space containing the material to be deposited — the “target.” The surface of the target is eroded by high-energy ions within the plasma, and the liberated atoms travel through the vacuum environment and deposit onto a substrate to form a thin film.

E-beam evaporation allows the evaporation of a wider range of metals with higher melting points off a graphite crucible. The process uses an electron beam to focus a large amount of energy on the source material in a water-cooled copper hearth or crucible. This produces a very high temperature, which allows metals and dielectrics with high melting temperatures (such as gold and silicon dioxide) to be vaporized, and then deposited on a substrate to form a thin film.

Thermal evaporation uses a hot filament or boat to evaporate materials such as chromium (Cr), germanium (Ge) or gold (Au). The process applies thermal energy from a resistive heat source to a solid-state material in a vacuum chamber, which evaporates the source. The vapor condenses on a substrate, forming a thin film of the source material. It is one of the most common, the lowest cost and the simplest forms of physical vapor deposition.

NanoFab PVD evaporation and sputter tools

Tool	Technique	Source	Size	Gases	Notes
Lesker 1	Magnetron sputterer	2 DC PS, 1 RF PS	6″ platen	Ar and N2 and O2	For approved materials
Lesker 2	RF sputterer	RF PS	9″ platen	Ar and O2	For ZnO and NiOx
Lesker 3	E-Beam	4-pocket hearth	12″ platen	Vacuum	For approved materials
Lesker 4	E-Beam	4-pocket hearth	12″ platen	Vacuum	No Cu, Au and Ag
Lesker 5	Magnetron sputterer	3 DC guns, 1 RF gun	8″ platen	Ar and reactive N2 or O2	No Cu, Au and Ag
CHA	E-Beam	4-pocket hearth	Planetary, 18 – 4″ wafers	Vacuum	For Al and Al/Si only
Edwards	Thermal	2 sources	8″ sample holder	Vacuum