Moving parts: Applied Materials as a MEMS tool supplier


with Tom Stepien
Click here to enlarge image

Applied Materials is a well-known supplier of processing and inspection equipment to the semiconductor manufacturing industry, and now also the photovoltaics (PV) industry. The company recently received a relatively large order for four tools from Silex, a leading foundry of MEMS devices. We caught up with Tom Stepien, VP and GM of Applied’s 200mm systems business, to get his take on what’s going on in the MEMS market, and what kind of unique equipment and process challenges MEMS devices present.

Q: It seems as though MEMS has been long considered a niche market. With the size of this recent order, is MEMS finally becoming its own industry?

For MEMS specifically, there have been some consumer applications–the Wii, i-phone, Guitar Hero–that have driven some of the increase. In consumer handhelds there are accelerometers and gyroscopes, both of which are MEMS devices. There have also been laws in the US and some pending laws in Europe that are notable. It was September of last year when the US tire pressure sensor law went into effect, and there are now hundreds of millions of units of tire pressure sensors being built worldwide. Meanwhile, Europe is looking at a stability control law to make sure the vehicles stay stable. Both examples, the consumer and automotive applications, have helped increase the volumes.

Q: Those devices can be pretty complicated with beams and moving parts...are there different manufacturing requirements? Do you have to configure the equipment differently and develop different process technologies?

Some MEMS requirements can be more demanding than traditional semiconductor devices. Some of the etches can be more intense; they can be longer and have to be more precise to get cantilevers perfectly aligned, because the mass at the end of the cantilever has to be very balanced for an air bag, for example. On the vias and on the trenches, you have very high aspect ratios, and there are some specifications on the sidewalls and the smoothness of the sidewalls which is often a tradeoff with etch rate. You also have to worry about the uniformity across the entire wafer–it’s pretty easy to get the uniformity in the center of the wafer, but the real trick is to have uniform process results across the whole wafer.

A second area that’s different is wafer handling. Wafers are sometimes thinner for MEMS applications and can require access to the backside, especially for pressure sensors where you have to build a diaphragm. You actually wind up processing on both sides of the wafer–you process one side and then flip it over and etch from the other side. So of course you don’t want any scratches or other defects to be introduced in the processing.

For some MEMS devices you do the micromachining at a wafer level as opposed to a die level. Of course that induces all kinds of stresses and you have to be careful about managing those stresses.

Another difference is inspection and test. You want to try to test MEMS devices in as close to real-world conditions as possible. Unlike traditional semiconductor devices, these have moving parts. The testing at higher temperatures at faster throughput and greater accuracy all make it more difficult on the testing side of things.

Challenging MEMS feature etched with Applied Materials’ Centura DPS DT+ etch system.
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Q: Is there interest in moving to a 300mm platform?

The majority of MEMS production today is still at 6 in. and below, but we are seeing migrations to 8-in. [200mm] as a way to reduce costs.

As MEMS volumes are growing, customers are looking to add capacity, and going to 8-in offers several advantages. At 8-in. you have access to technology that doesn’t exist at 6-in. in terms of either hardware or processes. There is also an integration aspect to CMOS where you’re on the same die or at the same package level.

There’s also the reliability factor of the equipment. Applied is continuing to invest in 8-in. If you’re a manufacturer looking to go to 8-in., you have these tools that have much better uptime and much better availability. They have a much more mature design, and you have more process knobs compared to 6-in. That’s where the Applied value proposition really wins, because we have thousands and thousands of these tools out there for the last 20-some odd years. As MEMS starts to become mainstream, we’re getting looked at for some of those requirements.

Q: How many tools does a MEMS manufacturer typically need?

Of course it depends on their business and what they’re making, what steps they’re handling. On the order that you referenced [Silex], that was etch, deposition (CVD and PVD), and planarization tools. Many of the top MEMS foundries as well as the captive guys have Applied tools, but it all depends on the volumes. If you’re making inkjet heads by the millions and maybe even billions, that’s a little bit different than some of the newer applications like the silicon microphones or the microfluidics medical devices which are still pretty early in terms of volumes.

Q: But in any case, you’re seeing this as a growing and important business that’s attractive to you as an equipment supplier?

Absolutely! The other thing that’s interesting to us is that large foundry customers are making big efforts in terms of getting into MEMS, especially integrating with CMOS devices. That’s another encouraging sign of growth.

Q: Are they developing specific processes for MEMS or are they trying to have the fabless guys come up with ways to use the existing process technologies and materials?

Some of the foundries have to adapt some of their processes to meet the needs of the MEMS devices. There are some unique metals that are typically used where they have to try to get the MEMS device to work with the current materials they have available in their foundry. There are unique etch requirements so they are having to either fine-tune what they have or bring in additional equipment to meet those needs.