Introduction

The Fabricated Products Group of H.C. Starck has several years of experience in the manufacture of high performance materials, particularly refractory metals like rhenium, niobium, tantalum, tungsten and molybdenum.

As one of the world’s largest producers of tungsten, tantalum metal and molybdenum metal powder, H.C. Starck supplies various solutions for the thin film industry, for applications such as photovoltaic cells for solar power.

High Tech Recycling of Refractory Metals

H.C. Starck has the capability to extract many refractory metals through a recycling process. The recycled tungsten, tantalum and molybdenum metals from spent sputter targets is just as high in quality and purity as that of the raw material.

The use of recycled material helps to conserve natural resources, and reduces energy consumption, thus serving as a vital part of a stable raw material supply.

Properties of Refractory Metals

The key properties of refractory metals used for thin film applications are:

• Low residual stress at optimum sputter conditions

• Thermal expansion coefficient similar to silicon

• Resistant to the diffusion of impurities

• Improved adhesion to substrates and subsequent layers

• Resistant to the harsh etchants

• Non-magnetic

• Conductive and can be easily sputtered

Tantalum

The tantalum products supplied by H.C. Starck have a uniform, high density microstructure and controlled texture that ensures superior sputtering behavior and uniform sputtering rates.

The products are available in six different grades of tantalum, with available purities ranging from 99.95% to 99.995%, to meet the requirements of different applications. Tantalum is widely used in chemical processing and the pharmaceutical industry, in addition to thin film PVD applications.

Tungsten

Tungsten is supplied in purity levels of up to 99.99%, in pure and alloy form. Tungsten's high density means that it is widely applied in the thin film coating industry.

Molybdenum

H.C. Starck supplies molybdenum in the form of powder and also as finished parts. It finds use in LCD displays, integrated circuits and photovoltaic solar cells.

Niobium

Niobium thin film is commonly used for optical applications. Like tantalum, this metal also has high resistance to chemical attack and corrosion.

Titanium

Titanium is a highly corrosion resistant metal with good electrical resistivity. It can be used in optical coatings, solar cells and LCDs.

H.C. Starck also produces other materials like molybdenum-titanium, molybdenum-niobium-zirconium, molybdenum-tungsten, nickel-chromium, and nickel-vanadium.

Applications of Refractory Metal Thin Films

The refractory metals are used in a number of industries as given below:

• Flat panel displays – The ultra pure materials serve as electrodes, adhesion, or diffusion layer in coatings used for TFT-LCDs used in GPS systems, cell phones, computer monitors and TV screens.

• Electronics and data storage – The sputtering target materials can be used for the manufacture of integrated circuits and optical data storage devices such as CDs and DVDs.

• Electrodes: Molybdenum is chosen for its resistivity and good ohmic contact property.

• Photovoltaic (PV) solar energy industry - Rotary and planar sputtering target materials made of high purity molybdenum can be applied for CdTe and CIGS- based solar cells while rotary NiV targets are used for Si thin film solar cells.

• Diffusion barriers: Tantalum, molybdenum, and tungsten thin film layers can prevent inter diffusion between two materials in electronic devices.

• Optical coatings: Reactively sputtered tantalum and niobium films have low absorption and high refractive index. The purity and uniformity of H.C. Starck rotary target materials enables coaters to achieve excellent control of each separate deposition process.

Conclusion

As a worldwide leader in refractory metals right from inorganic chemicals to finished product,H.C. Starck features state of the art laboratories and highly skilled professionals to develop new and innovative products for the future. The Thin Film Materials Lab of the company is equipped with magnetron sputtering equipment, film stress tester, adhesion tester, vacuum annealing equipment, spectrophotometer, 4-point resistivity probe, and scanning electron microscopes.

For thin-film PV applications, H.C. Starck delivers rotary and planar sputtering target materials made of high-purity molybdenum for CdTe and CIGS based solar cells, and rotary NiV targets used for Si thin-film solar cells. The company also produces niobium, titanium and other materials.