How to Make a Nickel Vanadium Sputtering Target?

In the process of preparing nickel-vanadium alloy, vanadium is added into the nickel melt to make the prepared alloy more conducive to magnetron sputtering, which combines the advantages of the nickel sputtering target and the vanadium sputtering target. With the progress of society and the development of semiconductor industry, the demand for nickel-vanadium target materials in electronics and information, integrated circuit, display and other industries is increasing.

Sputtering target materials are mainly used in information storage, integrated circuit, display, automotive rearview mirror and other industries, mainly used for magnetron sputtering various thin film materials. Magnetron sputtering is a method to prepare thin film materials. The ions generated by ion sources are accelerated to gather into a high-speed ion current in vacuum, which is bombarded by the accelerated particle flow to the surface of the object to be deposited. Kinetic energy is exchanged between the ions and the atoms on the surface of the object to be deposited. Nanometer (or micron) thin films are deposited on the surface of the object to be deposited. The bombarded solid is the raw material for deposition of thin film by sputtering method, known as sputtering target material.

In the fabrication of integrated circuits, pure gold is generally used as the surface conductive layer, but gold and silicon wafers are easy to generate AuSi low melting point compounds, resulting in the interface bond between gold and silicon is not strong, people proposed to add a bonding layer on the surface of gold and silicon wafers, usually pure nickel as the bonding layer, but the nickel layer and gold conductive layer will also form diffusion. Therefore, another barrier is needed to prevent the diffusion between the gold conductive layer and the nickel bonding layer. Barrier layer needs to use high melting point metal, but also to withstand a larger current density, high purity metal vanadium can meet the requirements. So in the production of integrated circuit will use nickel sputtering target, vanadium sputtering target, gold sputtering target and so on.

In the process of preparing nickel-vanadium alloy, vanadium is added into the nickel melt to make the prepared alloy more conducive to magnetron sputtering. Combined with the advantages of the nickel sputtering target and the vanadium sputtering target, the nickel layer (bonding layer) and vanadium layer (barrier layer) can be sputtered at one time. Nickel-vanadium alloy is not magnetic, which is conducive to magnetron sputtering. In the electronics and information industry, it basically replaces the pure nickel sputtering target material.

Characteristics and application of Nickel-vanadium alloy targets

Nickel-vanadium alloy target material is mainly used in solar energy industry, electronics industry and other fields. The application and required purity of nickel-vanadium targets are shown below.

1) Optical storage: 3N.

2) Solar film cell :3N.

3) Flat panel display coating :3N-4N.

4) Electronics and semiconductors :3N5.

5) Building glass :2N7.

Characteristic requirements for nickel - vanadium alloy sputtering target

Sputtering nickel-vanadium target requires high purity, less impurities, uniform chemical composition, no segregation, no pores, uniform grain structure, grain size is micron, and the difference in grain size in a single sputtering target is as small as possible. In this way, the magnetron sputtering is not easy to produce discharge phenomenon, and the magnetron sputtering film is uniform.

1. Purity

Sputtering target first of all is to high purity, because the impurities in the sputtering target has the greatest impact on the performance of the magnetron sputtering film, so we should reduce the impurity content of the sputtering target as far as possible, many domestic and foreign semiconductor or electronic product manufacturing enterprises on the sputtering target impurity content put forward high requirements.

2. Impurity content

The impurities in the sputtering target are strictly required. The content of Cr, Al and Mg impurities in the nickel-vanadium alloy sputtering target does not exceed 10ppm. If the content exceeds 10ppm, the corrosion performance becomes worse. The content of U and Th is not more than 1 ppb, and the content of Pb and Bi is less than 0.1 ppb. If the content is more than this, the electron charge will be adversely affected and the fault will occur. When N content is between 1 and 1 00ppm, the increase of N content will result in poor corrosion performance, so the content of impurities should be strictly controlled.

3. Density

Sputtering target material has very strict requirements on internal pores, because the pores in the target material will affect all aspects of the performance of the sputtering film, and the abnormal discharge generated in the process of magnetron sputtering will affect the photoelectric performance of the magnetron sputtering film. Therefore, the target material is required to have a higher density. In addition, the high density and high strength sputtering target can better withstand the thermal stress generated by magnetron sputtering. The preparation process of nickel - vanadium sputtering target is generally divided into powder metallurgy and melting. The sputtering target prepared by powder metallurgy method has more pores and low density. Smelting methods are divided into ordinary smelting and vacuum smelting. In the ordinary smelting method, the gas in the atmosphere is easy to enter the melt in the smelting process, resulting in the melting ingot gas content can not meet the requirements of sputtering target. Therefore, the preparation of nickel-vanadium sputtering target alloy is generally made by vacuum melting method, which can ensure that there are no pores in the material.

4. Grain size and grain size distribution

Nickel-vanadium targets need to go through multiple cold and hot processing processes, and the prepared target billet has a polycrystalline structure. The grain size is strictly required, and the grain size should be controlled within 100 microns. From the perspective of sputtering performance, for magnetron sputtering targets with the same chemical composition, the sputtering rate of small grains is faster than that of large grains. At the same time, the more uniform the grains inside the target, the more uniform the thickness of the film sputtered onto the silicon wafer.

Preparation of nickel - vanadium alloy target

In nickel-vanadium alloy, a slight change in the amount of vanadium will obviously change the properties of nickel-vanadium alloy. As a result, the Ni-V alloy can not be obtained by subsequent processing of sputtering target material. The typical Ni-V alloy composition is Ni-7V. The key to producing high purity Ni-V alloy is:

1) High-grade metal raw materials nickel and vanadium must be used, the purity of which must be above 99.95wt%. The purity of nickel raw materials can reach 4N5(99.995wt%) or even 5N, but the purity of vanadium raw materials is generally only 2N5-3N(99.5wt%-99.9wt%). The purity of vanadium limits the purity of nickel - vanadium alloys.

2) The melting point of vanadium is 1 91 9± 2℃, which is a refractory metal, and the melting point of nickel and vanadium is very different (about 336℃), so it is difficult to prepare the target material cast ingot with uniform composition by general melting method. In special applications, nickel and vanadium are first obtained by vacuum melting (electron beam or vacuum arc remelting (VAR) or vacuum induction melting (VIM)). After repeated vacuum melting, the total purity of alloy ingot is improved.

3) The introduction of impurity elements is strictly controlled in the preparation process.