E-Beam Evaporation System

Electron-beam evaporation is accomplished by using a high-energy beam of electrons to locally heat a material, even refractory ceramics, above its vapor pressure. The system at OSU is used primarily for deposition of ACTFEL phosphor layers, but is also used in deposition of p-type trasparent films and dielectrics. E-beam evaporation is preferred to sputtering in that dopant or coactivator concentrations can be easily varied either by thermally coevaporation or by preparing differently doped pellets. This process is much simpler, faster, and cheaper than preparing multiple sputtering targets, and has dramatically reduced phosphor development time.

The e-beam evaporation system is capable of thermal co-evaporation from two sources simultaneously, and e-beam evaporation from three sources sequentially. A crystal oscillator thickness monitor is used to determine rates of evaporation and total resultant layer thickness. A diffusion pump and LN2 cold trap make chamber pressure below 1 microTorr possible. Halogen quartz lamps are used for substrate heating.

RF Sputtering System

This system is a modified CPA radio-frequency sputtering system which is used to deposit oxide- and sulfide-based phosphor materials, p-type conductors, and occasionally high-dielectric constant dielectric materials. Sputtering is particularly useful for depositing multinary compounds, which are very difficult to evaporate due to the different vapor pressures of the constituent elements.

The system is equipped with two 2" rf magnetron sputtering cathodes, produced by AJA and Angstrom Sciences, which are driven using a 500 W rf power supply. Processing atmosphere is controlled through four mass flow controllers and throttling of the diffusion pump. A residual gas analyzer (RGA) is used to monitor levels of unwanted gaseous species (chiefly H2O). A load lock helps maintain high-vacuum integrity while a LN2 cold trap minimizes water contamination. Two halogen quartz lamps provide heating to the substrate holder to over 300 °C. The substrate holder can be scanned in front of the sputtering cathode to minimize nonuniformity.

Ion Beam Sputtering System

The Veeco ion beam sputtering system establishes a DC glow discharge from which ions are extracted and directed towards a target of the material to be deposited. This system is currently used to deposit thin films of Cu, Ti, SiO2, and ZnO, and ITO from 6" targets.

ARE System

Activated Reactive Evaporation (ARE) is the thermal evaporation of a substance in the presence of an activated gas (from a plasma). The system makes possible the deposition of oxide materials which are too refractory to be directly thermally evaporated. Unlike sputtering, separate targets do not need to be fabricated in order to vary stoiciometry or doping. High deposition rates are also possible compared to other deposition techniques.

The ARE system consists of three thermal evaporation sources, and electron cyclotron resonance (ECR) plasma source and microwave power supply, a substrate heater and controller, crystal oscillator thickness monitor, and leak and throttle valves for gas flow control.

Semi Group PECVD System

Chemical vapor deposition (CVD) involves introducing a number of process gases into an evacuated chamber. These gases chemically react to form a film at the surface of the substrate. In plasma-enhanced CVD (PECVD), a plasma is used to promote the reaction, resulting in lower process temperatures.

The PECVD system in the ECE cleanroom is equipped with mechanical and cryo pumps, a substrate heater capable of heating to 375 °C, four mass flow controllers for process gas control, an automatic rf power matching network, and a computer interface for programmed process control. We use PECVD primarily to deposit top insulator layers of SiON for ACTFEL devices, using N2O, N2, and SiH4. This system is a compromise between the large bandgap of SiO2 and the higher dielectric constant of Si3N4.

Veeco Thermal Evaporation System

Thermal evaporation is perhaps the simplest thin-film deposition method. Current is passed through a refractory boat or filament, resulting in resistive heating. Material in the boat or in a crucible held by the filament is heated to vaporization. The vaporized material redeposits onto the substrate, resulting in a thin film.

The Veeco thermal evaporator has three evaporation sources, crystal oscillator thickness monitor, and reaches pressures below 1 microTorr for high quality film deposition. The system is presently used primarily for solid source layer diffusion doping of ACTFEL phosphors.

Polaron Thermal Evaporation System

This system is basically a small desktop version of the above system and is used exclusively for deposition of Al or Au for device contacts.