As MEMS device topologies become more complicated, new photoresist deposition technologies will be needed. We recently spoke with Bennett Bruntil, Director of Electronics and Advanced Energy at Sono-Tek Corporation, about his company's experience with ultrasonic coating techniques. In this comprehensive interview, Bennett compares ultrasonic coating with traditional spin coating, and discusses market trends and emerging applications. He also comments on the most challenging MEMS device topographies, as well as Sono-Tek's product development roadmap.
MEMS Journal: Aside from high aspect ratio MEMS and sensors device structures, are there other applications for your ultrasonic coating system where it is more advantageous than traditional spin coating techniques?
Bennett Bruntil: Spin coating is a standard technique and works well in most cases, however it does have limitations and our technology provides a solution when working beyond its capabilities. Other than photoresist deposition, one of the quickly growing applications for our equipment is depositing a protective film onto wafers prior to dicing or polishing. Conventional high speed spin coating technology can often break fragile MEMS structures and/or may not be capable to provide a thick enough coating for effective protection. Our technology can create thick conformal films when needed between 5 to 75um, and beyond.
In addition, manufacturers look to our technology when the fundamentals of spin coating become too limiting. For example, when substrates are too large, irregular, have macro topography, or if there is a need to coat several individual wafers/substrates at a time. Customers often see a side benefit when they switch from spin coating -- a vast reduction in material consumption. Whereas spin coating typically has a 10% material transfer efficiency, we flip that number around with approximately 90% transfer efficiency.
MEMS Journal: What are some of the examples of the most difficult MEMS device topographies which you've encountered?
Bennett Bruntil: Our technology is able to apply conformal photoresist coatings onto challenging three-dimensional topographies such deep V-grooves, mesas, and through-wafer etch cavities. These are all areas where high speed spinning often encounters limitations. The feedback we get from our customers is that they are commonly able to achieve 3:1 aspect ratios and sometimes ratios as high as 5:1.
MEMS Journal: Have you done quantified analysis on how much is usually saved by using your systems in terms of the photoresist material costs and how these savings compare to the higher cost of your system?
Bennett Bruntil: The majority of customers are purchasing our ultrasonic coating systems for process advantages and the material savings is a great side benefit. With roughly 80-90% photoresist reduction, some of our customers do have a break-even ROI in less than one year.
MEMS Journal: What is the cost of your system? If there are multiple options, please briefly describe the options along with the corresponding costs.
Bennett Bruntil: While the SPT200 is a premium cost investment over traditional high speed spin coaters, it is very competitively priced for the market. Our photoresist coating systems are sold for both R&D as well as production volume coating and range between $80,000 and $140,000.
MEMS Journal: What kinds of materials can your system dispense? What kinds of materials cannot be handled by your system?
Bennett Bruntil: We can spray all photoresists that we have encountered so far, including positive and negative. Since most resist materials are developed for spin coating, they have much higher solids content (because 90% is spun off) than necessary for spray deposition. Wafer manufacturers commonly dilute conventional photoresist made for spin, primarily in order to achieve the correct coating thickness for spray deposition. When we spray, we use a lower solids content to achieve the desired coating thickness (since about 90% stays on the substrate). Aside from photoresist, our technology can spray most any material that meets two requirements: has a viscosity lower than 100 centipoise, and does not have undissolved particles above 10um in size. With a few exceptions, we can spray anything that meets those requirements.
MEMS Journal: What's on your product development roadmap for the next couple of years?
Bennett Bruntil: At this point in product development we are listening to what the market, but most importantly, our customers have to say about the new SPT200 system. Most of the products we create and develop (including the SPT200) are based on customer input and requests to fulfill the challenges they see with existing technology. I am very proud of the work done by both our design and application engineering teams on this system. We have a group of 5 application engineers who have first-hand knowledge with these applications, and are continually working with customers to help understand and solve problems. It was a true collaboration between our application engineers and design engineers at Sono-Tek, who worked together to deliver a system that addressed our customers’ challenges.
MEMS Journal: What are some of the most challenging customer applications which you've seen recently?
Bennett Bruntil: Every year new innovations in the MEMS marketplace push the limits with complex three dimensional structures. Our team is constantly overcoming these new challenges with more precise and uniform methods of photoresist deposition.
MEMS Journal: In which geographic locations are you selling the most units? And where are you seeing the most growth?
Bennett Bruntil: Since the SPT200 is fairly new we do not have much data here, but based on sales of our previous systems for the same applications we see the bulk of business in North America, China, and Europe. Growth in recent years has been driven mostly from China-based manufacturers, but we do see a trend of increased investment in the US marketplace also.
MEMS Journal: How much business have you done in China? What has been your experience there?
Bennett Bruntil: China has always been an interesting marketplace for Sono-Tek. Of recent, we have seen some deceleration in the China economy, causing a small dip in sales from that part of the world. Typically Sono-Tek will release our more advanced products to the China market after releasing them in the US and Europe, to help protect the proprietary nature of our systems. Having a China strategy is important for all high tech US-based companies, and the appropriate strategy is not always obvious.
MEMS Journal: Which events did you guys attend this year? Which one was your favorite and why?
Bennett Bruntil: Sono-Tek attends several of the SEMICON events each year, and our technical team always enjoys the US show with its technical conferences.
MEMS Journal: What are you main market segments? What percentage of your business is currently with MEMS customers?
Bennett Bruntil: Sono-Tek has a wide variety of market segments for our coating systems. Some of these include precision coatings onto medical devices, advanced energy products, semiconductors, PCB manufacturing, glass coating machinery, emerging functional nano-coatings, and a wide range of industrial coatings. MEMS is a significant contributor for Sono-Tek, and is definitely one of our growing business segments.
This article is a part of MEMS Journal's ongoing market research project in the area of MEMS manufacturing technologies. If you would like to receive our comprehensive market research report on this topic, please contact Dr. Mike Pinelis at email@example.com for more information about rates and report contents.
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