University of Kansas researchers have developed a novel apparatus and associated method for the in situ formation of multi-layer thin film structures using atomic layer deposition (ALD) and ultra-high vacuum (UHV) physical/chemical vapor deposition.
Conventional ultra-high vacuum (UHV) processes like physical vapor deposition (PVD) and chemical vapor deposition (CVD) are used for fabricating thin films at high temperature and/ or high vacuum conditions. Components for emerging technology devices, however, require material layers so thin and precise that they must be controlled at the atomic scale. Superconductor-insulator-superconductor (SIS or "Josephson junctions") and metal-insulator-metal (MIM) tunnel junctions are excellent examples.
ALD is a refined CVD process in which a thin film is built from alternating monolayers deposited by sequential pulses of different precursor materials. The self-limiting chemical reactions involved allow precise control over the thickness and composition of the film and provide uniform and conformal coverage that eliminates "pinhole" defects that cause leakage between layers. This presents a promising technique for certain aspects of thin film fabrication, but the required temperature and pressure necessitates a chamber separate from the one used in the UHV processes that create other layers of thin film structures. To avoid the contamination risk of transferring the sample between different chambers, an in situ transfer is desired. The present invention provides a cost-effective ALD module that can interface with existing UHV equipment.
This invention has been used to create ultrathin, low-leakage SIS tunnel junctions that are useful for quantum computers applications. The integrated ALD+PVD system also provides a powerful fabrication approach for many other nanostructured devices, including advanced energy devices (ultracapacitors, lithium ion batteries, graphene composite transparent conductors), magnetic data storage (MRAM), detectors and sensors (UV, infrared, gas, chemical), and electron and x-ray emitters.
HOW IT WORKS:
In Dr. Wu's lab, the novel viscous flow ALD reactor was connected to a multigun UHV sputtering system via a load lock and a magnetic transportation rod. The sputtering and load lock chambers share Ar, N2, and O2 gas lines. The ALD system has an independent gas delivery system and is heated externally with a resistive heater controlled by a variac. A system of solenoid and needle valves was designed to isolate and control the pulses of reactant gases.
This invention facilitates the research and development of atomic-scale engineered thin film structures, advancing the state-of-the-art in information and energy-related technologies.
WHY IT IS BETTER:
This invention provides a cost-effective alternative to commercial systems that integrate ALD and PVD capabilities for in situ transfer during thin film fabrication. The ALD module allows multiple precursor sources and can handle wafers up to 3" diameter with high uniformity. Its interface allows integration with an existing vacuum system directly or via a load lock. This method of fabrication has the capability to provide high quality thin film structures, as well as conformal coating of 3-dimensional surfaces.