An Overview of Tantalum Sputtering Target Material

Tantalum sputtering target material is a chip of tantalum obtained by pressure processing. It has high chemical purity, small grain size, as well as good recrystallized structure and consistency of three axes. Tantalum sputtering target is mainly used in optical fiber, the semiconductor chip and integrated circuit sputtering deposition film, as well as in cathode sputtering coating, high vacuum suction active material, etc., which is an important material for thin film technology.

Classification of the tantalum target

According to the application field, it can be divided into optical tantalum target and semiconductor tantalum target.

Tantalum-Sputtering-Target
Tantalum-Sputtering-Target

The performance index of the tantalum target

  • Purity

Metal impurities do not affect the sputtering process but affect the life of tantalum film, and the purity of the target material is different in different application fields. The impurities U, Th, and other radioactive elements have a negative impact on MOS, while K, Na and other alkali metals have a negative impact on MOS interface performance. In addition, transition metals such as Fe, Ni, Cr and refractory metals such as W, Mo, and Nb generate leakage current at the interface. Therefore, the content of the above impurity elements should be strictly controlled.

  • Porosity

The target material should be dense enough. If there are pores in the target material, the gas in the pores will be released in the sputtering process, and an arc will be generated, causing tiny particles to sputter out of the target and generating uneven points on the film.

  • Grain size

The size of grain affects sputtering uniformity and sputtering speed. Typically, the grain size is required to be less than 100 microns, since the large grain size causes uneven sputtering and irregular nodules on the target. Meanwhile, no crystal band is allowed and the grains should be uniform on the whole target surface.

  • Texture

The texture difference has a great influence on sputtering speed, and (100) texture is usually required.

  • Surface finishingment

If the surface finish of the target material is not high enough, it is easy to form small bumps in the sputtering process.

  • Uniformity

Uniformity should be consistent in all directions of the target and between each target.

Tantalum-target
Tantalum-target

Applications of the tantalum target

In recent years, with the rapid development of semiconductor technology, electronic devices are becoming more and more miniaturized and integrated, and the thin film technology is used in the manufacturing process.

Tantalum target is mainly used for sputtering coating. Tantalum film, tantalum alloy film, silicon tantalum oxide film, tantalum nitride film, and tantalum oxide film have a wide range of applications. Tantalum oxide is used in the resistance and capacitance of integrated circuits and the resistance of hybrid circuits; tantalum film forms a barrier layer to prevent corrosion when spraying printed circuit; tantalum film is also used as seed in magnetic resonance devices. The total global demand in these areas is about 30t annually.

Another major use of tantalum is as a diffusion barrier between silicon and copper conductors in integrated circuits. Compared with other metals, tantalum, as a barrier layer of copper, has a lower diffusion rate, higher interlayer bonding strength, and heat resistance. The global demand for sputtering targets in this application field is expected to increase to 200t.

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Applications of Tantalum in the Electronic Industry

Tantalum and its alloy have a high melting point, corrosion resistance, excellent high-temperature strength and free of radioactive etc, are widely used in the electronics industry, chemical industry, aerospace, weapon system, and the medical field, etc. Applications of tantalum materials in the electronic industry mainly include tantalum capacitors, integrated circuits, electron tubes, storage devices, and passive devices.

Tantalum Capacitors

Tantalum capacitors have strong corrosion resistance and can maintain stable electrical and physical and chemical properties under various environmental conditions. In addition, it also has a high resistance rate (7.5 x 1012 Ω cm), a large dielectric constant (27.6), and small leakage current.

Tantalum Capacitors
Tantalum Capacitors

Tantalum has the characteristics of valve metal, and the dense oxide film generated on its surface has unidirectional conductivity, which is suitable for capacitors. Tantalum capacitors are large in capacity and small in volume. Their capacitance is three times that of aluminum capacitors, while their volume is much smaller than that of aluminum capacitors. Tantalum capacitor has a working temperature range of 80 ~ 200 ℃, so it can meet the demand of different temperatures. In addition, tantalum capacitors also have strong stability and heat resistance, which makes them highly reliable materials in the electronics industry, as well as widely used in military and high-tech fields that need to ensure high reliability.

Integrated circuit

Tantalum has been introduced into the semiconductor industry as a barrier layer film material to prevent the diffusion of copper atoms to silicon wafers. Copper does not form a compound with tantalum and nitrogen, so tantalum and tantalum base films are used as a barrier layer to prevent the diffusion of copper. In order to prevent copper atoms from diffusing into silicon matrix, tantalum nitride, tantalum silicide, tantalum carbide, tantalum nitride silicide, tantalum nitride carbide, and other tantalum base films are used as barrier layers with good effects.

Tantalum-based films have high conductivity, high thermal stability, and excellent corrosion resistance, which are highly resistant to foreign atoms.

Tantalum
Tantalum in Semiconductor Chips

Memory device

Tantalum oxide based resistance variable memory (RRAM) has the advantages of simple structure, fast reading and writing speed, strong miniaturization and compatibility with the CMOS process. Tantalum oxide material has good thermal stability that can reach 1100 ℃. There are only two stable phases between the tantalum and oxygen, namely Ta2O5 TaO2, which also have two very high oxygen capacity ratio under the high temperature of 1000 ℃.

Passive device

When tantalum nitride film is exposed to air, an oxide layer will naturally form on the surface to protect the film from erosion in the presence of water vapor and voltage. Tantalum nitride chip resistors do not cause catastrophic failure of the device due to poor package or protective coating integrity.

At present, the application field of capacitor grade tantalum wire is further expanded with the rapid development of the electronic market. However, the development of tantalum capacitors has been greatly restricted due to various reasons, such as the increase in production cost, the further consumption of resources and the intensified competition among ceramic capacitors.

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