Deposition: Pulsed Laser Deposition System

EMSL's pulsed laser deposition (PLD) system is designed for epitaxial growth of oxide, ceramic, or synthetic mineral thin films and is composed of the following:

• An electro-polished stainless-steel chamber pumped via a turbo molecular pump and backed by a rotary scroll dry pump
• An excimer laser (KrF) for excitation at 248 nm
• Three standard mass flow control units for precise and reproducible process gas flow during deposition
• An electron cyclotron resonance (ECR) plasma gas source
• Reflection high-energy electron diffraction (RHEED) for real-time monitoring of the surface structure and morphology
• A continuous compositional spread control system for combinatorial synthesis using up to three different targets.

The PLD system is capable of growing uniform, multilayer, or compositionally spread combinatorial complex-oxide thin films with abrupt interfaces.

System Configuration and Operational Overview

Ablation plume during PLD deposition

PLD sample chamber

The PLD system was customized and manufactured for EMSL by PVD Products Inc. (loosely based on the PLD/MBE 2000™) and modified to include microwave plasma assistance and in-situ film growth monitoring capabilities. The ultra-high vacuum (UHV) multi-target manipulator holds up to six individual targets, ranging from 25 mm to 52 mm in diameter; provides continuous target rotation up to 40 RPM; and offers target indexing operated either manually or with a computer-controlled motor. A water-cooled top shield reduces the radiative thermal load on targets, manipulators, gears, and bearings. The sample manipulator will hold one 2-in. diameter substrate or multiple small samples for deposition on a variety of substrate sizes and shapes. The system is equipped with four individual gas source lines for inert or oxidative process gases. Plasma-assisted laser molecular beam epitaxy can be performed in the PLD system using an ECR gas plasma source.

PLD using a multi-target carousel is particularly suited for multi-component oxide thin films, complex oxides, multilayers, delta-doping, and combinatorial thin films. Films (and layered structures) of uniform composition can be deposited from a single target, or from multiple targets ablated in sequence. In addition, combinatorial synthesis using up to three separate targets can be easily achieved through computer control, resulting in a continuously varying, one- or two-dimensional composition spread across the substrate surface.

Plasma-assisted laser molecular beam epitaxy (OPALMBE) can be performed in the PLD system using an ECR gas plasma source. The system has six target holders and four individual gas source lines. The sample manipulator will hold one two-inch diameter substrate or multiple small samples, allowing the opportunity to coat a variety of substrate sizes and shapes.

The maximum growth temperature is ~1000°C in up to 1 atm oxygen for non-transparent substrates and 950°C for transparent substrates, with no thermal paste or bonding required. The working base pressure of the growth chamber is lower than ~1x10^-8 Torr. The Intelligent Window maintains a clear optical beam path over multiple sample depositions, extending longevity. Coupled with a load-lock for easy sample entry, the Intelligent Window allows extended-use periods without venting for maximum cleanliness.

A sophisticated computer control system enables flexible and reproducible growth of thin films, heterostructures, multilayers, and compositional spread samples. The computer control system allows control of target motion, substrate rotation, substrate temperature, mass flow control (MFC) rates, pressure, laser functions, and laser beam rastering. Using the TorrRHEED™ system, surface structure, morphology, and growth rate can be monitored in real-time at pressures up to ~50 mTorr.

Researchers may operate this system independently and can be trained for fully self-directed operation.

Microwave Plasma Unit

PLD system and excimer laser

The plasma unit is a UHV-compatible plasma source (PCS-ECR) for the generation of atoms and ions (SPECS GmbH). The absence of a hot filament to create the plasma permits operation with most gases, including oxygen, nitrogen, and hydrogen. This plasma unit is equipped for use as an atom/ion hybrid source with electrodes for extraction of variable kinetic energy ions from plasma.

Excimer Laser

The KrF pulsed laser (Lambda Physik Model COMPexPro 102), which emits 248 nm light, is a medium, average-power laser for material processing, science, and medical systems. With a handheld keypad that includes user-friendly function keys and an LCD display, operation is simple. Integration with PLD system control software is accomplished via the standard RS232 remote port. Using a fully contained, interlocked protective housing allows safe operation of the laser by preventing the possibility of exposure to eyes or skin.

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