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This article was originally featured in the edition: 2018 Issue I

Brewer Science Delivers Next-gen DSA And WLP Solutions

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Traditional CMOS scaling faces compound lithographic challenges at each new node. Brewer Science’s materials experts are reducing complexities and improving performance through new directed selfassembly innovations, while enabling packaging advancements with its temporary wafer bonding portfolio for WLP. Whichever direction the industry pivots, Brewer Science offers solutions

The road to next generation semiconductors becomes increasingly complicated at each new node. Geometric CMOS scaling worked well through 28nm, but today’s 14/10 nm devices typically rely on double or quadruple-patterning solutions plus a litany of other complex techniques to create transistor elements, manage edge roughness and control pitch. Getting smaller isn’t getting any easier.

Major semiconductor manufacturers pursuing greater density, high efficiency and better performance have pinned their hopes to extreme ultraviolet (EUV) lithography for transistors below 7 nm. But development complications have repeatedly pushed the introduction of EUV to succeeding generations.

Intel, Samsung, TSMC and other major fabs have indicated they will introduce EUV at 7-5 nm by the end of this decade. But what comes after 5nm? Will it be affordable and flexible enough to fit wide-ranging circuit requirements? This is uncharted territory where no one can risk multimillion, let alone multibillion, dollar/pound/euro investments.

Many manufacturers are actively seeking alternatives to EUV for myriad reasons including the fact that cost/benefit ratios that have favored incremental lithographic technique enhancements are getting much harder to calculate. As sophisticated tools have driven costs up sharply, manufacturers need mutigenerational benefits to commit resources. Many seek alternatives to market requirements or have explored alternative scenarios to leverage existing capital investments. Some shifted part of their capacity to manufacturing micro electromechanical systems (MEMS) devices that do not depend on 300mm wafer fabs or the most advanced process technology, showing it is possible to create value and strong revenue streams while diversifying product portfolios.

Brewer Science (Rolla, Missouri and worldwide) has been supporting advanced lithographic materials and process technology requirements since 1981 when company founder and CEO Terry Brewer created and delivered antireflective coatings that enabled new lithographic solutions—foundations of today’s industry standards. The company continues to pioneer new technologies, including its significant work with temporary wafer bonding (TWB) and debonding solutions.

“In backend manufacturing, we look for technical problems where the material solutions for existing requirements do not meet the future needs of our customers. We offer advanced material solutions that go beyond present day customer requirements by also offering a clear advantage in terms of process simplification, yield improvement and/or throughput enhancement," said Ram Trichur, Director of Wafer Level Packaging Business Development at Brewer Science Inc.



TWB process flow showing all major methods of temporary bond release.

Brewer Science’s temporary bonding and debonding techniques are especially applicable in fan-out wafer-level packaging (FOWLP). While the ‘chip-first’ approach has been in high volume manufacturing for some while, the ‘chip-last’ approach is still developing. Brewer Science sees many of its product solutions as offering a complete range of options for customers, whichever approach they are taking.

TWB has become the technology of choice for most applications in which a 300 mm silicon wafer is thinned, flipped and temporarily mounted on a carrier after which its backside is further processed on the road to producing 3D integrated circuits. Creating and handling thinned wafers is a challenging process; however, thin wafer-based devices allow for better heat dissipation, reduced form factors, greater performance and less power consumption. But thinning involves risks including fragility, stress leading to warpage or cracks, and thermal expansion match issues. After thinned wafers receive backside processing, the temporary mount needs to be smoothly dislodged (debonded) and device wafers need to be cleaned before subsequent processing. Manufacturers typically utilize one of three main approaches to safely and cleanly dislodge a temporary bond: thermal slide, mechanical or laser.

Brewer Science has supported temporary bonding/debonding requirements across multiple device generations and is one of the few companies to support every major type of physical debonding approach. Their products continue to evolve and now include fourth generation solutions for laser systems; they have succeeded in raising the temperature range of these processes up to 350°C.

“We have almost 15 years of experience in temporary bonding materials development and commercialization for the manufacturing of 2.5D, 3D, compound semiconductor, fan-out and other process flows. We realized very early that one product or even one platform of temporary bonding materials may not be suitable for all of the processes used in advanced packaging applications. Each process flow or device type has a unique set of requirements, and we offer a broad portfolio of bonding materials and release layers designed to support these individual processes. This approach results in maximized customer benefits in terms of delivering simple processes with high yield and low cost of ownership," said Trichur.

The company is seeing growing interest in the latest generation of tools, especially across Asia and most notably in China. While all customers see benefits, some report rather remarkable results, especially when they had previous solutions that were not delivering as needed.

“All of our customers benefit from the advances we deliver, yet some have particularly striking success stories. A manufacturer that was producing compound semiconductor devices and bonding with wax materials had a total yield loss of around 30 percent during backside processing due to the poor thermal and mechanical properties of wax. We introduced a new temporary bonding material, and their yields subsequently increased to over 99%," said Trichur.

Other new device architectures are key to many companies’ strategies to either delay or bypass the need for expensive EUV transitions. A new technology seeing widespread development work on the road to commercialization is directed self-assembly (DSA). Brewer Science partnered with Arkema (Grenoble, France) in 2015 to bring first-generation DSA materials to the commercial marketplace. Arkema is a high-performance materials specialist with a global presence and 2016 sales of 7.5 billion euro. The companies’ collective goal is to ultimately support device geometries down to 5nm and below so that regardless of the path to next-generation devices that manufacturers choose, Brewer Science will have an advanced solution enabling faster throughput, higher yield and superior performance.

At the SPIE Advanced Lithography 2018 conference (February 2018), Brewer Science announced that it had achieved a new milestone in the support of commercial-quality DSA materials. Brewer Science’s new OptiLign™ system includes three DSA materials: block copolymers, neutral layers and guiding layers that Brewer Science and Arkema believe provide a cost-effective path to advanced node wafer patterning processes for feature sizes down to a 22 nm pitch.

“Taking OptiLign materials from pilot line to commercial-scale production represents the next significant milestone in making DSA a viable option for semiconductor manufacturing," said Dr. Srikanth (Sri) Kommu, executive director, Semiconductor Business, Brewer Science Inc. “Historically, the industry has relied on equipment enhancements to reach the next technology node. Now, materials solutions are stepping in to provide that edge and extend tool capabilities. The OptiLign product family is an example of this paradigm shift."

Brewer Science’s OptiLign family of DSA products provides all the materials needed for self-assembly. Block copolymers define the pattern. Neutral layers allow the pattern to be formed on each layer. Lastly, guiding layers give the material directional orientation. All the materials are designed to work together for optimal performance, and are dependent on material and surface energy.

Through its partnership with Arkema, Brewer Science has tapped into a way to deliver DSA materials that allows for consistent feature sizes via a unique polymer production process. Critical to high-volume manufacturing is the fact that this new process enables the type of scaling needed to support an entire technology node, as well as unique polymer quality and reproducibility, all of which sets OptiLign materials apart from competing solutions.

Block copolymers (BCPs) are polymers containing two (or more) polymers joined together that will spontaneously segregate when coated and annealed on a neutral layer. The neutral layer has a surface energy that both blocks will adhere to equally; hence the name neutral layer. However, the features naturally created by BCP are random, so a “guide" is needed to make the BCP go where circuit designers wish.

There are many process flows for guiding the BCP, including creating physical features and aligning the BCP between them (graphoepitaxy), or treating the surface to create areas of the neutral layer that have a preference for one section of the BCP in order to align them (chemoepitaxy). Depending on the BCP and guiding method that are used, DSA can be used to create lines, holes, pillars, and other features.

“Feature size is built into the molecular structure of the DSA materials and can vary from batch to batch, so securing a sub-nanometric reproducibility can be challenging," explained Dr. Ian Cayrefourcq, Director of Emerging Technologies, Arkema. “Arkema’s special process for formulating large batches of polymers of the same size allows Brewer Science to supply a fab with consistent feature sizes for the technology node’s life span."

In July 2017, Brewer Science announced that it had extended its relationship with Arkema to further work towards next-generation DSA materials. Brewer Science scientists have been able to reduce the feature size by 20% compared to the first-generation materials, another milestone towards the ultimate goal of supporting 5nm and smaller features. This benchmark is important since most industry experts agree that extending device scaling without relying on EUV or complex multi-patterning schemes is essential to any new technologies’ ultimate success. And DSA offers even more benefits.

“DSA represents a lower-cost and higher-throughput solution over EUV, but another big cost advantage lies in the reduced mask requirements. DSA still needs lithography and etch processes, but these are lower cost compared to multiple patterning. EUV masks are a significant part of the EUV step cost. DSA also offers a technical advantage in that it can reach lower feature sizes now (compared to) other patterning technologies," said Hao Xu, Director of Semiconductor Business Development at Brewer Science.

Xu also believes that major fabs which have already committed to EUV may conclude that combining DSA with EUV will better support their ultimate goals.



Brewer Science Gen4 TB-DB process flow.


“DSA and EUV are complementary because smaller pitches can be printed with EUV that are not accessible with immersion litho. Smaller pitches means two things: lower multiplication factors can be done with DSA, which leads to a lower possibility for defects. Also, there is the possibility of eliminating the trim etch step in the chemoepitaxy flow when using EUV. EUV can also provide graphoepitaxy templates for contact hole multiplication. It is also important to note that because of the resolution limitations of EUV at smaller nodes, it is possible that DSA will help stretch out the timing for, or even eliminate, the need for high-NA (numerical aperture) EUV tools," Xu added.









9nm lines formed using Brewer Science’s next-generation OptiLign™ DSA materials.


Conclusion

Brewer Science enabled key developments in semiconductor photolithography with its introduction of antireflective coatings. The company grew and expanded to offer a wide range of advanced solutions for global semiconductor manufacturing. Today, Brewer Science products and services support all major approaches to advanced lithography, thin-wafer handling and 3D integration as well as chemical and mechanical device protection and products based on nanotechnology. In its quest to support nextgenerational / emerging technologies, Brewer Science enables 3D advanced semiconductors through its temporary wafer bonding (TWB) and debonding product lines.

Its latest Gen4 solutions for laser-based applications have elevated working temperatures to 350°C. Recognizing the potential of directed self-assembly (DSA) to revolutionize advanced device fabrication, Brewer Science partnered with Arkema in 2015 to introduce commercial-ready OptiLign™ materials for DSA features down to 22 nm pitch.

That partnership, extended in 2017, is positioned to continue innovation with next-generation solutions for even smaller DSA features; on-going work targets supporting devices to 5nm and below. As manufacturers seek alternatives to multi-pattern lithography that are less complex and costly, or for those seeking to delay or augment extreme ultraviolet (EUV) lithography, Brewer Science offers alternatives that extend device scaling while reducing costs, increasing performance and simplifying complex advanced node manufacturing.



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