Although the rotary targets have developed in recent years, the mainstream shape of the sputtering target is still the planar type. Today let us take a look at the pros and cons of planar targets to help you determine whether a planar sputtering target is suitable for your project.
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Advantages of Planar Sputter Target
Simple structure &#; one of the main advantages of the planar target is that the structure is simple. The common planar targets on the market are rectangular planar targets and circular planar targets, which are easily produced by molds. In other words, planar target preparation requires fewer machines and technologies and is easier to prepare. This is why planar targets still dominate the sputtering target market.
Low price &#; You can never deny that the price is always an important competitive factor. As mentioned above, the manufacturing process of the planar sputter target is easier, so its price is much lower than the rotatory sputter target.
Strong versatility &#; Planar sputtering targets usually have strong versatility. Therefore, the transportation of the planar targets is relatively simple and is not easily damaged during transportation.
Good uniformity and repeatability &#; Film layers sputtered by planar targets usually boast good uniformity and repeatability. Planar targets are still best suited for prototype work or elemental experimentation, especially when large amounts of material are not needed at once.
Disadvantages of Planar Sputter Target
Its biggest disadvantage is the low utilization rate (generally only about 20%). In the sputtering process of the planar target, a strip-shaped pit will be formed when the target of the glow region (the magnetic field distribution region) is consumed to a certain extent, making the target body thinner. And once the pit depth reaches a certain value, the target cannot be utilized anymore. The low utilization rate also reduces its price advantage to some extent.
In conclusion, planar targets are still the best choice for prototype work or elemental experimentation, especially when large amounts of material are not needed at once. But its disadvantage of low utilization rate (20% vs. 80% compared with the rotatory target) does constrain its development.
Next week, let us look at the biggest competitor of the planar target&#; the rotatory target. Weighting the pros and cons of these two types of sputtering target may help you better choose the one for your application.
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SAM Sputter Targets
Stanford Advanced Materials (SAM) Corporation is a global supplier of various sputtering targets such as metals, alloys, oxides, ceramic materials.
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One approach to cathode placement during sputtering is a planar configuration, in which the cathode is mounted directly above the substrate. This is the preferred method for applications where uniformity is paramount to performance.
Benefits of Planar Cathode Placement
When you mount the cathodes directly above the substrate during thin film deposition, you&#;ll achieve:
- Excellent thickness uniformity control: Because the cathodes are directly above the substrate, and not at an angle, sputtering with this configuration leads to excellent thin film uniformity. The target is also significantly larger than the substrate, which eliminates any edge effect to ensure uniformity. And while uniformity can be improved in other methods (for example, by rotating the substrate), planar placement offers the best uniformity control without any other adjustments to the configuration.
- Uniform thin film quality: Additionally, since every point on the substrate is the same distance from the cathode, the film properties themselves (sheet resistance, index of refraction, etc.) will tend to be highly uniform.
- Improved yield: Achieving uniform thin film properties leads to a higher yield, which is an important factor for cost of ownership.
- Good lift-off capability: For good lift-off, you need a highly collimated, directional sputtering process that is perpendicular to the substrate&#;s surface. You can achieve this with a planar configuration that has the proper system geometry.
- High throughput: Planar cathode mounting also delivers a high throughput for sputtering, because it allows you to sputter the entire surface of the substrate at once. For high-volume applications, planar cathodes can be used in a cluster tool for maximum throughput and efficiency.
- High deposition rate: Planar mounting of the cathodes helps ensure an appropriate throw distance to the substrate, compared to confocal sputtering, which often requires a farther throw distance to fit in multiple cathodes at an angle. A shorter throw distance leads to higher deposition rates, so a planar cathode configuration helps optimize process efficiency.
Tradeoffs to Consider for Planar Cathode Placement
While the above benefits may be very important for your application-specific needs, there are several important tradeoffs you need to consider with this approach.
- Limited to one material at a time: Unlike confocally mounted cathodes, which can co-sputter multiple materials at the same time, the planar cathode method only allows for one material to be coated at a time. If co-sputtering is not a key process requirement, then this is a tradeoff you can afford to make. However, if you do need to coat with multiple materials or multiple layers, this method may not be very efficient for you, and would end up hurting your throughput if you don&#;t use more than one chamber. A cluster tool with more than one chamber solves this, but requires a larger capex investment.
- Target cost: Your individual target costs may go up compared to the confocal sputtering method, which only requires the targets to be about half the diameter of the substrate. With planar mounting, you&#;ll need a target that&#;s actually larger than the substrate to ensure that the coating covers the entire surface. While the target cost per substrate coated is about the same, if you are coating precious metals such as gold, it may require a significant investment.
- Efficiency of material transfer: To achieve high uniformity with planar cathode mounting, much of the target material will end up on the shields. If you&#;re depositing precious metals, such as gold or platinum, you&#;ll likely be sacrificing in terms of your cost of ownership. If your material is relatively inexpensive, then this may be a tradeoff worth making, but it&#;s something important you&#;ll need to consider if you&#;re aiming for efficiency of material transfer. This also needs to be weighed against uniformity requirements for a higher yield, which has an impact on cost of ownership.
Confocal cathode positioning is another approach used for sputtering, and can help address some of these tradeoffs if you have major concerns for your application requirements. Read our blog post on the benefits and factors to consider for confocal cathode placement.
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