It’s hard to believe that inside such a non-descript building set back down a picturesque country lane in (almost) rural Indiana, really cool things are happening. This is the home of Dynaloy, LLC, a subsidiary of Eastman Chemical Company, where innovative chemical formulations are being developed to remove the most stubborn of photoresists and polymer residues left behind during semiconductor manufacturing process steps. Until recently, the importance of cleans as part of the 2.5D and 3D IC process flow has been largely ignored. So the Dynaloy team decided it was time to bring me in for a visit so I could learn first hand what its all about, and what differentiates Dynaloy from other chemical cleans companies.
The Flip Chip Story
As Steven Dwyer, business director of Dynaloy’s Electronic Materials division, explains it, Dynaloy was first established in 1964 as a manufacturer of industrial solvents offering a wide range of materials to a wide range of customers. They forayed into the photoresist strip business with the advent of flip chip technologies and the development of its FlipStrip product line for Flip Chip International (FCI). FCI subsequently licensed its bumping technology to the major outsourced semiconductor assembly and test houses, and by association, Dynaloy was catapulted into the semiconductor manufacturing industry as a key supplier to major bumping houses. In 2011, Eastman Chemical Company acquired the company in a strategic move to bring Eastman into the semiconductor industry.
The Key is Customization
What differentiates Dynaloy from other photoresist manufacturers is that the company specializes in formulated chemistries vs. straight solvents. “We’re known in the industry as the people who can solve your problems,” explained Diane Scheele, market development manager, Dynaloy. “We ask customers questions like ‘what is the problem? What are you removing? What are the limitations? What is the next step in the process?’ From there we determine the starting point formulation, then test it and tweak the balance of the components to suit the specific problem.”
But that is just the beginning. Kim Pollard, Technology Manager, explained the company’s mission to work with customers to develop unique formulations that are first pulled from a basic formulation toolbox. “Customers’ processes can affect the properties of the original resist formulation,” she explained. “Our job is to work with customers to remove the resist regardless of what the customer has done to it or what the underlying layer is. The challenge is taking one off without affecting the other.” Pollard explained about positive resists that are known to be easy to clean. However, a particular thick positive resist formulation used in copper pillar applications pose a cleaning challenge because it needs to stand up to electroplating and is subsequently difficult to remove. “The reasons why aren’t well understood,” she said. “It’s not as easy to clean as people expect.” This is a case for Dynaloy.
Seeing is Believing
A tour of the applications lab and demo by Mike Phenis, Senior Chemist, illustrated just how complicated finding solutions to particular challenges can be. Using various resist-coated coupons cut from the same wafer, he simulates actual cleaning process steps as closely as possible in a test environment. For my benefit, he performed comparisons between a dissolve formulation versus a swell-and-lift formulation (where the resist breaks up and lifts off the wafer) to show the removal process as well as the effects on the SnAg capped Cu pillar bumps.
Before screening the samples, we looked at them under the microscope to make sure we knew what we were working with. Next, Mike put each sample in a temperature-controlled beaker of solution using a proprietary holder specially designed for this purpose. Over time, the dissolving formulation removed more residue from tighter spaces without damaging the bumps. The swell and lift was initially more aggressive in it’s cleaning, but over time did not remove all the residue and damaged the bumps. In a parallel experiment, Mike showed the effectiveness of a dissolve formulation for removing polymer residue from TSVs. Simultaneously, he was also running climate related tests to see how various formulations hold up to extreme temperatures for shipping to manufacturing locations around the world.
The CoatsClean™ Tour
One purpose of my visit was to witness first hand, a novel cleaning innovation called CoatsClean™, which was nominated for a 3D InCites Award (link to nominee page). CoatsClean is not a formulation, it’s an entire process, which is a departure from regular procedure for Dynaloy. Originally developed by Eastman in 2009, CoatsClean was advanced to commercialization by Dynaloy in 2012, after being acquired by Eastman.
“The industry has become more material focused, where it used to be equipment based,” explained Dwyer. “But equipment is based on physics, and there’s only so far it can be pushed without integrating fundamental material science.” He explained that technology advancements such as FinFETS, TSVs, and 3D Cu pillars all require the right material properties for fabrication. For example, advancements in lithography were driven from a chemistry standpoint. And processes like chemical mechanical planarization (CMP) leave residues that stop a bond from forming. Chemistry is needed to remove that residue.
“Our product wheelhouse contains the formulations to remove organic films from hard substrates using any type of equipment; immersion, spray or a combination of the two,” said Dwyer. As such, Dynaloy has developed two product lines, Dynastrip™, which uses industry standard immersion and single wafer spray processes; and CoatsClean, which relies on 3 key elements: equipment, process, and chemistry. If you take one element out, it won’t work. The process is tool-specific, and the company has worked with EV Group to develop it. Eastman owns the process patent, which Dwyer says is unusual because the tool company usually owns it.
Here’s how it works: the resist-coated wafer is lowered into a micro-bath chamber, where 200ml of solvent is puddle-coated on the wafer surface. The wafer turns slowly to distribute the material. Next comes the secret to CoatsClean: a heater chuck lowers close to the surface of the wafer in the micro-bath without touching it, and heats the surface quickly and safely above the flashpoint of the material to accelerate its interaction with the photoresist. Following the heating step, a spray rinse with DI water removes the residue completely. And voila! clean, micro-bumped wafers. In conventional immersion systems, this process would take anywhere from 45-90 minutes. In this process, it takes 3-9 minutes, using 85% less chemistry than immersion baths. Additionally, so little material is used that there’s no need to recycle the chemistry or solvent disposal. This adds up to a greener, more efficient processes resulting in higher throughput and a lower cost-of-ownership (CoO).
The Road to Clean
Dynaloy’s clear mission is to increase its product base and expand into new areas of business and technology, explained Dwyer. “We’re good at cleaning Bosch process residue from TSVs for 3D ICs and MEMS applications,” he noted as an example. I saw the SEM with my own eyes. I have to say, it’s pretty impressive. They are also working on rework of passivation, and removal of temporary debond materials for 3D ICs.
“We respond to market pull, limiting projects so we know what to push,” said Pollard. She shared the company’s technology roadmap from 2011-2014 that illustrates the issues they see going forward and the challenges the company plans to find solutions for. “There’s nothing on the roadmap that we already haven’t considered in the lab,” she noted. Items on the roadmap aren’t limited to the development of formulations, but also adhere to fairly stringent HSE guidelines that fall into line with Eastman’s culture of environmental stewardship.
The company has achieved one goal for 2012, developing formulations for photoresist removal compatible with CoatsClean process. On the HSE side, they’ve developed formulations that eliminate the need for e-series glycols. Now in the works and ongoing are a number of projects with 2014 target completion dates including:
- Passivation, de-bonding, stress-buffer layer removal solutions
- Solutions with optimized III/V compatibility
- Post-Strip Solutions for Cu and control of Sn in Solution
- Post etch and post -Bosch etch residue removal solutions
On the HSE side of things, the company is working to eliminate TMAH, HA, and DMSO from its formulations. They are developing water-based formulations with improved dissolvability, as well as working towards low odor formulations.
Wrap-up
I came away with some very clear takeaways about the complexities of cleans from this visit. The bottom line, there’s a lot more to it than you think. After spending two days learning from this dedicated team, not to mention taking in a minor league ball game at Indianapolis’ Victory Field, its clear to me that not only is Dynaloy successful at developing stuff that works, they have a lot of fun doing it. I look forward to watching the progress of their robust roadmap unfold. ~ F.v.T.
