Insights from industry

Using Tantalum in Advanced Electronics and Semiconductor Chips

Tantalum is a crucial component in next generation semiconductors, allowing electronics manufacturers to produce chips of increasingly greater information densities. H.C. Starck are providers of high purity tantalum for use in the semiconductor industry, supplying it in several different forms designed for PVD sputtering.

Why is tantalum a desirable material for use in semiconductor chips?

Tantalum has very stable thermal, electrical and mechanical properties that extend over a broad range of temperatures for semiconductor processing. It’s compatibility with silicon and silicon dioxide for chip processing is a big benefit.

Functioning primarily as a diffusion barrier between a copper seed layer and silicon, tantalum engenders unique sticking properties for both silicon and copper without reacting chemically with the copper substrate. The diffusion barrier is often a multi-layered structure of pure tantalum, and tantalum nitride, which is reactively sputtered.

Tantalum’s versatility allowed high volume adoption in diffusion barrier applications for copper interconnects. While other materials could, in principle, be used for the same purpose, the rapid advancement in semiconductor technology and “Moore’s Law” (an observation that the number of transistors in a dense integrated circuit has doubled approximately every two years) have positioned tantalum as the preferred material with high stability and very few processing issues.

Titanium has been substituted in some cases, but its reactivity with copper has to be carefully controlled. Also, niobium and tungsten cause changes in mechanical, thermal and electrical properties of the semiconductor chips. The reliable performance characteristics of tantalum films remains a number one advantage in this rapidly developing environment.

The surface of a semicondcutor chip. Tantalums unique properties make it an essential component in advanced electronics.

The surface of a semicondcutor chip. Tantalums unique properties make it an essential component in advanced electronics. shutterstock.com | Zhukov

What are the different roles that tantalum play in Semiconductor technology?

In addition to the role of the diffusion barrier for copper interconnects, tantalum can be deposited as a pure metal, an oxide or a nitride.

The insulating properties of tantalum oxide are very beneficial when creating capacitors and the stable resistivity of the oxy-nitride can be used to form on-chip resistors.

Thermal ink jet printer heads benefit from the high modulus and chemical inertness (low corrosion) characteristics of tantalum and it is also used as structural material in the formation of the ink chamber itself. Tantalum when alloyed with aluminium has been used as the heater layer in older, thermal ink jet technology.

How is tantalum introduced to the semiconductor surface?

Tantalum is deposited via physical vapour deposition (PVD), in a process known as sputtering. Tantalum is sputtered either as a pure metal, or as a nitride in reactive sputtering.

There are two benefits to this. The first is that the purity of the sputter target material is maintained in the deposited film and second, the process is much easier to control than chemical vapour deposition (CVD).

Tantalum is very ductile and can be fabricated into plates that are either diffusion bonded for planar sputter systems, or formed into shapes such as the hollow cathode sputter target or radiofrequency coils (RF) coils.

A silicon wafer. PVD is used to coat the silicon, allowing a copper layer to be placed on top with no diffusion between the metal (copper) and semiconductor (silicon) layers.

A silicon wafer. PVD is used to coat the silicon, allowing a copper layer to be placed on top with no diffusion between the metal (copper) and semiconductor (silicon) layers. shutterstock.com | GrayMark

Why are diffusion barriers an important component of semiconductor chips? Why is tantalum often used for this?

The primary function of a diffusion barrier is to prevent contamination of the underlying silicon with the conductor material, either copper or aluminium.

Normally, titanium is used with aluminium and tantalum is used with copper. When titanium reacts with copper undesirable inter-metallics form, whereas in contrast tantalum and copper are entirely immiscible.

Tantalum and titanium also have great sticking qualities to silicon improving the adhesion of the copper or aluminium to the substrate. Both tantalum and titanium can be deposited in either pure metal or nitride conditions or a combination allowing the interface between the silicon and copper or aluminium to be fine-tuned to control the properties of the deposited seed material.

How is tantalum used in capacitors and what are the advantages of using tantalum capacitors compared to other competing technologies?

In bulk capacitors with a very high surface area, tantalum powder is sintered to form an electrically conducting mass, and the surface anodized to form a stable, insulating tantalum oxide layer on the surface.

Using this method a very high capacitance per unit volume can be achieved with very short electrical conduction paths. Because tantalum's electrical properties are very stable with temperature, the capacitance does not change much over the range of practical use.

This property becomes especially important in demanding outdoor applications, such as automotive and telecommunication industries. The short conduction paths allows very quick loading and unloading, allowing buffering of input and output signals from integrated circuits at all frequencies.

Capacitors on a motherboard. Tantalum capacitors facilitate a very high capacitance per unit volume and short conduction paths.

Capacitors on a motherboard. Tantalum capacitors facilitate a very high capacitance per unit volume and short conduction paths. shutterstock.com | Benson HE

Are other compounds of tantalum also used in integrated circuits and semiconductor chips? If so, what are they used for?

Other than the option of reactively sputtering an oxide, nitride or oxy-nitride, there are few applications for metal alloys of tantalum.

Tantalum oxide is a great insulator and has a high refractive index. While tantalum can be readily alloyed with tungsten, niobium or ruthenium, one of the greatest benefits of using pure tantalum is the recycling opportunity. More than 50% of the tantalum used in sputter targets returns to the semiconductor material process stream.

In what different forms does H.C. Starck supply tantalum?

H.C. Starck offers various grades of capacitor powders, crystallographic texture controlled plates, discs and shaped products for three dimensional sputter targets in purities ranging from 3N to 5N5.

In addition, we supply sputtering target plates for semiconductor, magnetic data storage, flat panel, LED and solar applications. H.C. Starck also provides tantalum and its alloys for a host of non-semiconductor applications in various forms: ingot, powder, rolled strip, welded tubing, alloy additive, bar, plate, sheet and rod.

The default specification is ASTM or AMS, but more detailed specifications can be provided on an application by application basis to ensure compliance to the customer’s exacting requirements.

The primary impurity in tantalum is niobium, which occurs naturally with tantalum in the ore. H.C. Starck’s tantalum and tungsten supply chains have been declared free of “conflict minerals” following regular, independent third-party audits conducted by the Conflict Free Sourcing Initiative (CFSI), a joint effort by the Electronics Industry Citizenship Coalition (EICC) and the Global e-Sustainability Initiative (GeSI).

H.C. Starck supply tantalum in many different forms.

H.C. Starck supply tantalum in many different forms. shutterstock.com | beejung

How important is the quality of tantalum used in semiconductor chips? How does H.C. Starck ensure that the tantalum they supply is of a high enough quality?

As chip technology advances, the thickness of deposited layers gets thinner and thinner requiring improved metal sputtering uniformity and particle-free process consistency.

The deposited thicknesses are now less than 50 nanometres, so impurities have a direct effect on the layer properties. Reducing impurity levels during the processing of tantalum is a cornerstone of H.C. Starck’s success.

Besides being EICC certified, a primary industry requirement is “ship-to-control” related to chemical consistency. H.C. Starck manages the input material chemistry from ore extraction through all the downstream operations in order to guarantee the chemical consistency of the cast ingot.

Melting parameters are carefully monitored to ensure the purification process eliminates undesirable elements and maintains tight statistical control of the batch. Following EB melting, thermo-mechanical processing is tightly controlled to develop the desired microstructure that provides consistent sputter deposition properties.

Consistent chemistry, fine grain size and consistent crystallographic texture are the hallmarks of H. C. Starck’s tantalum sputtering targets.

H.C. Starck’s strategy for procuring raw materials is based on two principles: the purchase of raw materials exclusively from suppliers with environmentally and socially sound business practices, and the continuous expansion of recycling activities.

The stringent, globally applicable procurement guidelines detailed in our Responsible Supply Chain Management System (RSCM) guarantees that H.C. Starck buys raw materials only from suppliers who comply with strict requirements with regard to environmental protection, occupational safety and social responsibility.

We take the position set out by the Electronic Industry Citizenship Coalition (EICC) and the Organization for Economic Co-operation and Development (OECD).

Regarding our recycling activities, H.C. Starck is one of the few companies in the world with the ability to reclaim all technology metals via recycling processes. We lead the world in tantalum recycling. Our expertise is based on many years of development and unique processes, and allows us to provide environmentally sound recycling without loss of quality.

With our closed-loop supply chain, practically all H.C. Starck products can be recycled after use. For the electronics industry, capacitors containing tantalum as well as tantalum and molybdenum sputter targets are likewise recyclable.

Does H.C. Starck assist their customers in the product development stage of tantalum containing-chips or offer customised tantalum products for specific applications?

Yes, H.C. Starck has a highly skilled R&D and Advanced Engineering staff knowledgeable in tantalum metallurgy and applications for sputtering process as well as capacitors, aerospace, defense and chemical process industry applications.

Tantalum has a range of beneficial properties that can be employed to solve critical problems. Its high melting temperature and strength plus its chemical resistance to corrosion makes it perfect for semiconductor applications.

In addition to the manufacturing capabilities, we at H.C. Starck have developed other capabilities such as finite element modelling, crystallographic and metallurgical analysis, mechanical testing and thin film deposition resources available in our state-of-the-art laboratories to assist customers in developing the desired characteristics of the tantalum, molybdenum, tungsten, niobium or alloy products.

A crystallographic scattering patten. H.C. Starck also provide a range of R&D services including crystallographic and metallurgical analysis.

A crystallographic scattering patten. H.C. Starck also provide a range of R&D services including crystallographic and metallurgical analysis. shutterstock.com | kois00kois

Are your customers using tantalum for any other exciting applications?

Absolutely! Tantalum’s immiscibility with copper and high ductility can be utilized as a diffusion barrier for A15 superconductor materials as well as acting as a strengthening and stiffening element in superconductor wires and cables.

For example, H.C. Starck’s tantalum is qualified as a diffusion barrier material for superconducting wires used in ITER, a major international nuclear fusion project.

Tantalum can be alloyed with tungsten to make it even stronger and still remain highly ductile giving its various uses in high performance chemical and aerospace applications.

It's chemical inertness, particularly near room temperature, makes tantalum compatible with the human body meaning it can be used in medical implants. Tantalum also has unique mechanical properties that can be fine-tuned for defence applications.

Tantalum can be supplied as alloys, solids or porous structures.

Tantalum can be deep drawn to form a variety of shapes for many applications. Tantalum powder can be used in a variety of additive manufacturing processes including laser bed, electron beam and cold spray deposition leading to even more exciting possibilities.

H.C. Starck has recently established capabilities to supply spherical tantalum powders with low interstitial content that are specifically designed for 3D printing processes.

H.C. Starck's tantalum is being used as a key component in ITER's experimental nuclear fusion reactor.

H.C. Starck's tantalum is being used as a key component in ITER's experimental nuclear fusion reactor. Source: ITER Organization

Where can our readers find out more about tantalum and H.C. Starck?

We have articles on AZoM as well as our H.C. Starck web site. Both brochures and product data sheets are found on the web site and can be downloaded. For more information, please contact us directly at [email protected]

About H.C. Starck

The H.C. Starck Group is a leading global supplier of technology metals and advanced ceramics. The company operates modern manufacturing facilities in Europe, America, and Asia and serves growing industries such as the electronics, chemicals, automotive, medical technology, aerospace, energy technology, and environmental technology industries, as well as engineering companies and tool manufacturers.

On December 31, 2017, the H.C. Starck Group had 2,600 employees in the United States, Canada, Great Britain, Germany, China, Japan, and Thailand.

H.C. Starck’s products are predominantly based on technology metals: Tantalum, Niobium, Tungsten, and Molybdenum.

The Fabricated Products Division converts technology metal powders into customized semi-finished and finished products through pressing, sintering, rolling, melting and thermo-mechanical processing and surface treatment.

The Tungsten Division provides high performance products for the mechanical engineering and tool making, automotive and energy industry, aviation industry, and the chemical industry, for example:

  • tungsten carbides for carbide tools and wear parts
  • tungsten and cast tungsten carbides for oil and gas drilling
  • tungsten metal powders for heavy metal alloys
  • tungsten chemicals as precursors for catalysts

The Advanced Ceramic Components (CER) Division manufactures specialized technical ceramic parts and films. CER produces engineering parts such as sealing rings, functional parts including fuel cells for solid oxide fuel cell (SOFC) systems and products for dental applications as well as for armor and wear protection. Furthermore, CER focuses on technological developments to expand the portfolio toward product applications in the semiconductor industry.

In 2018 H.C. Starck sold the division Surface Technology & Ceramic Powders to the Swedish Höganäs Group, effective March 1st and the division Tantalum and Niobium to the JX Nippon Mining & Metals Group, effective July 1st.

The group is led by a two-member Executive Board: Dr. Jens Knöll (Chairman of the Executive Board), Dr. Jan Lösch (Member of the Executive Board).

H.C. Starck was founded in Berlin in 1920. Since 2007, the company is owned by financial investors Advent International and The Carlyle Group.

H.C. Starck is registered in Goslar (Germany) and the Group’s headquarters is located in Munich (Germany).

H.C. Starck Fabricated Products

For more information on this source, please visit H.C. Starck Fabricated Products.

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Comments

  1. Bryan Tracy Bryan Tracy United States says:

    Hi-

    I am very interested in the "unique sticking properties".  
    Would you have a reference?

    thanks very much,

    Bryan Tracy
    Senior Director, Advanced Imaging
    EAG Laoboratories

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoM.com.

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