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Depositing consistent, high-quality thin films can be challenging. There are any number of factors that can affect yield and performance, but here are the top five challenges in thin film manufacturing:
- Poor Adhesion and Delamination
- Poor Film Quality/Contamination
- Equipment Inflexibility
- High Cost and Poor Scalability
- Substrate Incompatibility
More importantly, there are actionable steps to take in overcoming these challenges in thin film production.
Poor Adhesion and Delamination
Delamination, where the thin film layers peel away, is a significant cause of device failure and a major challenge in thin film manufacturing. This is especially true with flexible substrates, which are subject to the stress of being folded or bent.
Poor adhesion and delamination are the result of a variety of factors, including latent stress from the manufacturing process itself, surface contamination, material incompatibilities, environmental conditions, and operational wear-and-tear.
Pre-cleaning of the surface before thin film deposition can significantly improve adhesion. Pre-cleaning removes water molecules, hydrocarbons and other particles or contaminants from a substrate before the thin film coating is actually deposited. It can also remove cross contamination from previous deposition steps.
Certain pre-cleaning methods may also be used to micro-roughen the substrate, or to chemically activate the surface, which can improve adhesion in oxide films. Pre-cleaning can improve a thin film’s optical or electrical properties as well, which may be adversely affected by contaminants.
There are a wide range of approaches to pre-cleaning. Before deciding on a specific technology for pre-cleaning, there are certain performance, process, and budgetary factors to be considered. Read our blog post on pre-cleaning here. For a more in-depth overview, download our white paper, Pre-Cleaning in Thin Film Physical Vapor Deposition.
Stress control during the manufacturing process can also significantly reduce delamination. Stress in thin films can induce curvature in the substrate and impact film adhesion, and some deposition methods impart higher stress in the resulting films than others.
The tunable, independent control of ion energy and ion current density of Denton’s patented Endeavor RF Ion Source and Denton’s Plasma Ion Beam Chemical Vapor Deposition (PIB-CVD) process result in a wide process window that produces stress-free films for better adhesion and higher yield. The process can compensate for the stress and end up with a net-zero-stress film, even up to depositing an optical filter on a sheet of plastic, which did not curl up due to stress.
See this blog post, Denton Receives Patent for RF Ion Source, for more background information on the Endeavor RF Ion Source and the relationship between deposition and stress control.
Poor Film Quality/Contamination
Another major challenge in thin film manufacturing is maintaining consistent film quality and avoiding contamination. The quality and purity of a thin film can have a tremendous impact on device performance. In lasers, for example, contamination and poor film quality will reduce a laser’s maximum potential power.
One potential source of contamination is the deposition process itself. The highest quality optical films are typically produced by Ion Beam Sputtering (IBS), but, while traditional IBS systems provide good process control, high-energy ions can sputter from the target as well as other system components and shields. Such particulate contamination can lead to lower film quality.
By way of contrast, Denton’s proprietary Biased Target Sputtering (BTS) technology uses low-energy ions below the sputter threshold, thus preventing particulate contamination. To obtain sputtering, the target is given a large negative bias, typically 300-1200V. Since all of the sputtering energy comes from the target voltage, the ion beam profile is largely irrelevant.
BTS offers excellent control of thin film interfaces and provides independent control over ion currents and energies. This eliminates contamination and scatter from beam overspill, prevents surface damage, enables tight stress control, and creates dense, defect-free films.
For more background on BTS and how it works, read this blog post: Applications Enhanced by Ion Beam Biased Target Sputtering (BTS).
Equipment Inflexibility for Multiple Processes
One challenge often faced in thin film manufacturing is that the production process is often “baked in” to the deposition system itself, so that it becomes difficult to adjust the recipe to meet changing requirements. Once a system is in place, manufacturers are locked into a particular process.
The solution to this thin film challenge is to ensure any manufacturing equipment has the flexibility to tweak processes or even handle multiple different processes.
Denton Vacuum engineers its systems for maximum flexibility. First, as innovators in ion energy and plasma control, Denton offers unmatched control over ion energy. Most sources can produce some tunability of ion energy, sometimes over several hundreds of electron volts. But only Denton has technology that, from the same source, can produce high current density for both very low – 25 eV ions – as well as very high – 500 eV ions.
This enables the creation of a wide variety of film qualities simply by tuning the ion energy. Using a single precursor, HMDSO, Denton’s PIB-CVD technology is able to produce a polymer-like film and then, simply by changing the ion energy, deposit a diamond-like composite (DLC) film directly on top. From one precursor, Denton can produce two completely different films, simply by changing the ion energy.
Denton’s Versa cluster platform also enables tremendous flexibility and production efficiency in thin film manufacturing. For complex, multi-step processes, Denton’s Versa cluster platform can tie Denton’s Discovery, Infinity IBE, Infinity IBD, Voyager, and Integrity systems and components into a complete solution – integrated, optimized, and automated for a customer’s precise process. All of Denton’s thin film systems, ion sources, transfer hubs, pre-clean modules and process management systems are designed to fit together, and Versa provides the platform to tie them all together. Denton’s Versa cluster is also able to process different-sized wafers without requiring any retooling, providing tremendous process flexibility.
High Cost and Poor Scalability
Cost and scalability are a concern in any manufacturing process. Any thin film process decision must weigh the right balance of system cost, yield, throughput and film quality.
For example, evaporation is an ideal deposition method for large batch processing because it offers high deposition rates and can easily accommodate both large and small substrates. However, evaporation involves a relatively high amount of manual effort, limiting production scalability, increasing labor costs and possible quality control issues.
On the other hand, sputtering – especially magnetron sputtering – is repeatable and can be automated, making it ideal for high-volume, continuous production. Sputtering’s repeatability and automation compatibility enable scaling of manufacturing production with high yield and low labor costs.
Denton’s line of thin film deposition systems is designed for maximum scalability and optimal yield. From the desktop Desk V to the high-volume, large-area Phoenix, the same thin film deposition methods are available across the entire product line.
There is no single answer for improving throughput and reducing cost, especially across different deposition methods. For a deeper dive on this topic, read these blog posts: Thin Film Considerations for High-Volume Manufacturing, Increasing Throughput in Sputtering and Evaporation, and Is Evaporation or Sputtering Better for Your Application?
Substrate Incompatibility
Substrates provide the base upon which the thin film can be deposited. Thin film substrates include not only materials such as the silicon used in traditional computer chips, but also alumina, sapphire, quartz, and various technical glasses. Beyond such rigid materials, thin films are also commonly applied to flexible substrates like polyimide and liquid crystalline polymers (LCPs).
Substrates are chosen for each application for their unique properties, which can include high electrical performance, thermal conductivity, or mechanical stability or flexibility.
Temperature can be a major challenge in thin film productions, as not every thin film deposition method is compatible with all substrates. For example, many methods use high heat. In CVD, heat is applied to the substrate, and reactive precursor gases are then introduced which react with the heated substrate surface or combine to form new compounds that grow films on the substrate surface. The standard approach involves temperatures between 600°C to 800°C, which is far too hot for temperature-sensitive substrates.
Denton’s revolutionary Plasma Ion Beam CVD, or PIB-CVD, enables deposition at room temperature, as low as 20°C. There is no need for heat, preventing thermal damage to the substrate. This makes it possible to deposit on plastic substrates.
Size of the substrate can present another source of incompatibility in handling substrates. While 300mm (12 inches) is the most common wafer size for high-volume manufacturing for advanced logic and memory, 200mm (8 inch) and other wafer sizes remain common.
Direct handling of wafers during the thin film deposition process makes perfect sense for mass-producing wafers that are all of the same size. However, in the compound semiconductor industry and other industry segments, multiple wafer sizes are quite common. It is not economically viable to have separate production lines for each wafer size, so typically wafers of different sizes all go through the same system.
For these high-mix environments, it is critical to minimize system downtime for wafer size changes. By using wafer carriers instead of direct handling of wafers, this downtime is completely eliminated.
Denton’s wafer carrier systems are designed to accommodate any wafer up to maximum of 300mm. Because the wafer is placed in the carrier, and the system then moves the carrier through the process, the size of the wafer is immaterial. Because of this, Denton’s systems can run 3-, 4-, 5-, 6- and 8-inch wafers all in the same process run on the same tool, without changing tooling.
To learn more, read this blog post: How to Handle Varying Wafer Sizes in Compound Semiconductor Manufacturing.
Conclusion
While there are any number of factors that can affect yield and performance, working with Denton can overcome these challenges in thin film production.
For poor adhesion and delamination, pre-cleaning of the surface before thin film deposition can significantly improve adhesion. Stress control during the manufacturing process can also significantly reduce delamination. Denton’s tunable, independent control of ion energy and ion current density in Ion-Assisted Deposition with the Endeavor ion source result in a wide process window that produces stress-free films for better adhesion and higher yield.
For poor film quality and contamination, Denton’s proprietary Biased Target Sputtering (BTS) technology uses low-energy ions below the sputter threshold, thus preventing particulate contamination and delivering the highest-quality films.
For equipment inflexibility, Denton’s unmatched control over ion energy enables its systems to create a wide variety of film qualities simply by tuning the ion energy. Denton’s Versa cluster platform also enables tremendous flexibility and production efficiency in thin film manufacturing.
For high cost and poor scalability, Denton’s thin film deposition systems are designed for maximum scalability and optimal yield, improving total cost ownership (TCO).
For substrate incompatibility, Denton’s revolutionary Plasma Ion Beam CVD, or PIB-CVD, enables deposition even at room temperature. There is no need for heat, making it possible to deposit even on plastic substrates. For manufacturing environments that handle a variety of different wafer sizes, Denton’s wafer carrier systems can run 3-, 4-, 5-, 6- and 8-inch wafers all in the same process run on the same tool, without changing tooling.
To learn more about Denton and Denton’s full line of thin film systems, visit our website or start a conversation with us.