Influence of Sputtering Target Purity and Uniformity on Large Area Coating
The shape, purity, density, porosity, grain size, and binding quality of the target greatly influence the coating quality and sputtering rate. High-quality target material can ensure good film quality and extend the life cycle of Low-E products. More importantly, it can reduce production costs and improve production efficiency. Here we share the influence of target purity and material uniformity on large-area coating.
Effect of sputtering target purity on large area coating
The purity of the sputtering target has a great influence on the properties of the films. When the clean surface glass enters the high vacuum coating chamber. If the purity of the target material is not enough under the action of electric field and magnetic field. In that case, the impurity particles in the target material will adhere to the glass surface during the sputtering process, resulting in the film layer at some positions is not firm, and there is a phenomenon of peeling off. Therefore, the higher the purity of the target, the better the performance of the film.
In the research on 99.9% purity copper sputtering target, it is found that sulfur and lead are inevitable to be introduced into a Cu target's preparation. The addition of trace S can prevent the rough surface occurrence caused by the increase of grain size and microcracks during hot working. However, when the content of S is higher than 18 ppm, microcracks will appear again. With the increase of S and Pb's content, the number of cracks and the number of arcing discharge increases. Therefore, the impurity content in the target material should be reduced as much as possible. The pollution source of the sputtered film should be reduced, and the film's uniformity should be improved.
Control of sputtering target preparation process conditions
For targets with poor thermal conductivity, such as sial sputtering targets, heat transfer is often blocked due to impurities in the target. There is a difference between the cooling water temperature used in production and the coating line's actual water temperature, which causes the target to crack during use. In general, a slight crack will not have a great impact on coating production. However, when the target has apparent cracks, the charge is very easy to concentrate on the cracks' edge, which leads to abnormal discharge on the target surface. The discharge will lead to slag falling, abnormal film formation, and an increase in product scrap. Therefore, in the process of target preparation and controlling purity, we should also control the preparation process conditions.
Influence of sputtering target uniformity on large area coating
For alloy sputtering target materials, there are often uneven distributions of materials. Such as aluminum agglomeration in Si-Al target, aluminum segregation in zinc aluminum target (the atomic mass of aluminum is 27 less than the atomic mass of zinc 65. Aluminum will float up during the cooling process after pouring, resulting in high aluminum content on one side and low aluminum content on the other side). Because of the low melting point, the agglomerated Al in the sial target is very easy to drop slag in sputtering and film formation, while the amount of Al added in the spraying process is certain. Some agglomerations indicate that the aluminum content in other positions is less, which affects the sial target's thermal conductivity and conductivity. So the sputtering rate is inconsistent, the uniformity of the film is poor, the target cracks, and the target discharge is intensified. It also reduces the film quality. The segregation of the target composition will affect the sputtering rate (film uniformity) and film composition. Therefore, in addition to controlling the purity of the target material, the distribution of the alloy target material is also crucial.
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