This is part of our New Materials are Getting Thinner and Thinner series. In case you missed it, start by reading part 1 and part 2.
What is metallization?
Metallization is the process of adhering a thin metallic film to a surface. While electroplating technologies have been around for centuries, newer technologies are required to deposit a thin layer of metal on a carrier surface.
GIXRD experimental pattern
Chemical vapor deposition
Chemical vapor deposition (CVD) is a process in which a film is deposited from the vapor phase by the decomposition of chemicals on the surface of a substrate. The deposition of the film is controlled by a chemical reaction and is more versatile than many traditional deposition methods. The nature of the chemical precursor is used to control the phase deposited and to control its structure. This allows for both conformal and large-area growth, enabling the possibility of achieving, reproducibly, very high levels of purity in the materials.
Physical vapor deposition
Physical vapor deposition (PVD) uses a physical means to deposit a thin layer of material, with several steps performed under high-temperature vacuum conditions. A solid precursor material is gasified, typically using high-power electricity or laser, and then moved into a reacting chamber where the coating substrate is located. Source material atoms then stick to the substrate, forming a thin coat.
PVD is used as the deposition method to produce an extremely hard, corrosion-resistant coating. Thin films made with PVD have a high-temperature tolerance and resistance to separation from the substrate. PVD is also considered an environmentally friendly process.
Inkjet assisted metallization
An emerging technology for the manufacture of photovoltaic cells is inkjet assisted metallization, which offers an alternative to conventional photolithographic thin film technology. This method can provide low-cost, fine-resolution reduction in process complexity by direct inkjet patterning, avoidance of degradation of p-n junctions by firing at low temperature (350 °C), and uniform line film on rough-surface solar cells. The metallization process involves jet-printed metallo-organic inks, belt furnace firing and thermal spiking. With titanium thin film underlayer as an adhesion promoter and multilayer inkjet printing, solar cells of 8.08% average efficiency without AR coating can be obtained. This efficiency value is approximately equal to that of thin film metallized solar cells of the same lot.
X-ray diffraction of thin metal films
A critical step in manufacturing materials is the ability to characterize the material for research, quality control and troubleshooting material failures. Several laboratory techniques are available to characterize thin films. Each technique yields important aspects regarding the chemical and structural information about the thin film. Many instruments, particularly TEM, XPS and SIMS, cost hundreds of thousands of dollars and are situated in dedicated research laboratories. X-ray diffraction (XRD) is a cost-effective means of characterizing the crystalline composition of materials and is available in portable, benchtop and floor-standing formats.
Using Bragg’s Law of X-ray diffraction, XRD is a primary technique in the identification and characterization of compounds based on their diffraction pattern. Any material can be modeled as a mixture of both ordered and disordered parts; the largely ordered parts of the material are called crystallites and the largely disordered parts are called amorphous. An investigation on structural properties of a material measures the degree of order or disorder in the atomic placements inside the sample.
Generally a bulk technique, XRD can use grazing incidence technology (GIXRD) to characterize thin films. GIXRD uses small incident angles for the incoming X-ray beam making the technique surface sensitive. Distances are in the order of nanometers. Below (typically 80%) the critical angle of the surface material studied, an evanescent wave is established for a short distance and is exponentially damped. Therefore, Bragg reflections are only coming from the surface structure.
The crystallographic structure of multi-functional inorganic and hybrid organic-inorganic thin films (nanometer scale) have been characterized by GIXRD. This analysis is important as electronic and optical properties strongly depend on the structure of compounds. In GIXRD a fixed grazing angle (~0.5° – 2° Ω) is used to exclusively measure the layer and not the substrate.
Another variable in designing thin film materials for various applications is the thickness of certain layers. One standard technique for determining the thickness of thin layers is X-ray reflectometry (XRR), which is based on the interference between X-rays reflected on different layers in the material.
Our application scientists used grazing incidence XRD and X-ray reflectometry to distinguish between different structure types of amorphous and crystalline characteristics of a thin film nickel deposition on a silicon substrate sample.
This evaluation of the measurement allowed the determination of the layer thickness of the nickel with reasonable precision. Using the Thermo Scientific™ ARL™ EQUINOX 100 X-ray Diffractometer combined with the Thin Layer attachment created an easy-to-use system for basic thin film and coating investigations in industrial and academic research. This system also allows fast and easy QC/QA procedures at manufacturing sites.
To learn more, read our Investigation of Ni on Si thin film with ARL EQUINOX 100 X-ray Diffractometer for details.
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