Tegal Corporation: A Focused Approach

Tegal Corporation, headquartered in Petaluma CA, has provided etch tools to the MEMS manufacturing market since the mid-1990s. Chip Scale Review caught up with Paul Werbaneth at the MEMS Executive Congress, November 4 in Scottsdale AZ. and learned more about Tegal's history in the MEMS market, MEMS etch processes, and the company's business strategy.

CSR: How long has Tegal been involved with MEMS manufacturing processes?

Werbaneth: By 1996, when I rejoined Tegal, we were already involved in MEMS fabrication, handling plasma etch applications for some of the earliest inertial sensors being manufactured at the time. As MEMS device manufacturers began to include non-CMOS materials, such as PZT (lead zirconate titanate) and AlN (aluminum nitride), the MEMS etch applications continued to line up well with the etch technology Tegal had already developed for ferroelectric RAM (FRAM) fabrication. In addition to MEMS, Tegal also served the compound semiconductor fabrication space at this time, with a history as long, if not longer than we have in MEMS device fabrication. We'll see that our processing experience with Through Substrate Via etching from our compound semiconductor days has been invaluable to us in developing silicon Deep Reactive Ion Etching (DRIE) technology for today's Through Silicon Via applications.

CSR: Initially, Tegal Corp. served the semiconductor industry. Why did the company decide to shift focus from CMOS IC front-end etch applications to focus on the MEMS market?

Werbaneth: Around the same time we are talking about above, the mid-1990s , the CMOS IC industry made a push towards 300mm substrates. Our portfolio was focused on 200mm, and smaller, substrates and etch tools—even down to 3 inch wafers, in the case of compound semiconductors. It was apparent to us that the signal to move to 300mm wasn't clear, and would take significant investment to develop. So, instead, we decided to focus tools to process 3", 4" and 6" wafers, rather than tilt at the 300mm windmill. Beyond compound semiconductors, MEMS was the market that needed just such tools. Additionally, Tegal acquired our PVD division, Sputtered Films Inc., which offered deposition tools for metal and dielectric films that dovetailed nicely with our MEMS strategy. It's nice for me to remember, here at the MEMS Executive Congress 2010, that, as part of our effort to become part of the MEMS community, we joined the MEMS Industry Group in 2001 as a charter member.

CSR: Why has Tegal decided to focus its business strategy entirely on its core competency of plasma etch processes and get out of the deposition business.

Werbaneth: There are several strategies (thank you Michael Porter) companies can use to gain competitive advantage. The two most people think of are competing on pricing (lower) and competing on features (better, more). But there is also a third competitive strategy in the mix, that being to compete by being completely focused at what it is you do and, by focusing, become the best at what you do. When you're focused on one product line, in our case DRIE, you aren't distracted by other things that hinder you from really becoming the best in your field. Tegal decided to focus on our core competencies and develop technological advancements within the parameters of that.

CSR: Where do etch processes come into play with MEMS fabrication besides TSVs?

Werbaneth: Almost every MEMS device, or family of MEMS devices, requires deep silicon etch processes - whether you're fabricating inertial sensors, silicon microphones, image sensors, etc. Most of what we do is Bosch process based, the Bosch process being an plasma etch process, developed by Robert Bosch GmbH. That is absolutely the best way to etch deep, deep structures in silicon. With the Bosch process for deep silicon etching our silicon DRIE tools can handle the variety of features and shapes our customers throw at us, including slots, round holes, or sleeve structures, in the case of Through Silicon Vias (TSVs). We also have capability to do cryogenic (low temperature) etching of silicon, using a non-Bosch process, which allows us to form deep trenches with smooth sidewalls. Cryogenic etching of silicon may be better suited to optical MEMS applications where you're dealing with reflected or transmitted light. The smoothness, or not, of the silicon walls forming the ends of the structure affect how the light is handled.

CSR: Considering Tegal's long involvement in MEMS manufacturing, how have you seen the industry evolve and change and what tool adaptations have been necessary to keep up with this evolution?

Werbaneth: We've seen the MEMS industry move from low volume into high volume manufacturing. For Tegal, that meant our facilitating new DRIE tool requirement, such as manual wafer loading etch tools converting over to cassette-to-cassette fully-automated loading; single reactors on a system to multiple reactors for increased throughput; and from stand-alone systems that aren't factory automated to those that are connected to a company's factory automation system.

CSR: As we've discussed, Tegal's tools are primarily 200mm. What is your strategy with regard to expanding into 300mm?

Werbaneth: For the MEMS market, the days of 300mm are still a long way off. That said, we will soon offer a 300mm chamber and platform, coming from the work we are doing with TSV etch. In the 3D integration space we already have an active 300mm program, working together with our JDP partners in Europe. It's the right time now for us to look beyond 300mm JDP work, and to begin courting additional attention.

CSR: How are TSVs for MEMs different than TSVS for 3D ICs?

Werbaneth: Generally speaking, MEMS products don't contain CMOS transistors, unless you are a monolithic MEMS guy. However in 3D ICs, you're dealing with CMOS wafers that either already have transistors there (in via mid and via last processes) or transistors coming (in via first processes). Additionally, in via last TSV schemes, you have to deal with a wafer with multiple metallization layers, and multiple layers of dielectric, possibly low k dielectric, films. This presents different challenges and concerns than simply etching silicon itself. When you add the metal and dielectrics, the mechanical properties of the wafer change, and we need to be mindful of that. Additionally, and traditionally, for plasma etching applications in CMOS IC fabrication, we're always paying attention to ensure the plasma is not damaging the transistors.

CSR: One final question. How has Tegal leveraged its experience in MEMS to serve other markets, such as 3D integration?

Werbaneth: With our MEMS silicon DRIE experience, tool set, and depth of knowledge, we have a very solid stepping stone from which to move into TSV 3D IC applications. We're crossing the stream from the MEMS bank to the CMOS IC / 3D-IC side, and we're bringing everything we already know from all our years in MEMS with us, rather than starting from scratch.