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Feb 2019

How To Tackle The Top 10 Semiconductor Filtration Challenges Part 1: Maximize Die Yield, Filter Particles as Small as 1.5 nm

Today, the average computer chip is comprised of more than 10 billion individual transistors that require more than 1,000 steps to assemble into working components. To add to this complexity, the number of components in an integrated circuit doubles about every 18 months, according to Moore’s law. This adds up to a challenging landscape for manufacturers of semiconductor chips.

What’s more, estimates show that the loss of just one die per wafer can equate to more than U.S. $1 million in lost revenues each year. And, a major contributor of faulty dies is contaminant particles that travel along with gases and can be distributed onto the surface of dies.

Undoubtedly, as chips grow denser, line nodes become smaller. Only a few years ago, when average line nodes measured 22 nm, and a 3-nanometer particle made its way into the line, it wasn’t a show stopper. Today, defect-causing particles can be as small as 10 percent of the line node size; meaning, these days, a 2-nanometer particle spells disaster – in the form of a defective die.

We know that wafer process technicians agonize over ways to improve die yields by 1 percent or a fraction of a percent. In today’s sub-28-nm line nodes, much of the challenge lies in the fact that even the most sophisticated defect inspection systems can’t detect random defects caused by particles lodged in the etch trench on the surface of the wafer. So, oftentimes, the manufacturer doesn’t know there’s a problem until the wafer processing is complete. By that time, the company has invested a significant amount of time, money and effort into fabricating that chip.

Therefore, logically, an optimal solution is to ensure particles never make it into the process chamber and onto the chip (or, alternately, to minimize particle disturbances inside the process chamber). More on that in a future blog post.

A Scientifically Proven Method to Capture Particles as Small as 1.5 nm

A little over one year ago, Mott energized the industry with the introduction of a gas filter specifically designed and engineered for ultra-high purity semiconductor manufacturing processes.

These filters were scientifically tested in applications requiring gas flow rates ranging from 1 to 200,000 SLPM (standard liters per minute). Results showed they delivered 9-log (99.9999999%) filtration of particles down to 1.5 nm with confirmation at the most penetrating particle size of 80 nm. In simple terms, if there were a billion particles present in one cubic foot of gas entering this filter, only one particle per cubic foot of gas would make its way out of the filter.

Interestingly, what Mott’s research scientist, Dr. Ken Rubow discovered, is that, contrary to standard thinking, it wasn’t the smallest of sub-micron particles that were the most challenging to capture – it was actually mid-size, sub-micron particles that presented the greatest filtration challenge.

Using depth filtration and taking advantage of the behavior of sub-micron particles, filter designers know that different size particles in the gas stream behave differently. Large particles are more readily captured by filters because they have substantial size. And, smaller particles bounce dynamically through the filter’s many tortuous pathways until they are eventually captured. Mid-size particles, however, have neither size nor excessive movement, so they often are the most elusive.

What’s the Secret to Nano-Particle Filtration?

The secret to capturing particles successfully is to design a filter that contains a multitude of intricate, winding pathways with optimal surface area for capture.

Consider this: to successfully capture particles, you need ample time. If particles are moving through the filter too quickly, you fail to create diffusion, a result of Brownian motion or a bouncing-around effect, so particles will make their way through the filter uncaptured. Mott’s filters maximize the residence time of particles to ensure the highest filter efficiency at the smallest particle size; in short, ensuring gases flow at the proper velocity so particles can be captured effectively. To accomplish this, Mott has developed new metal filter medium using a variety of materials and alloys.

Mott’s new fiber metal filter technology maximizes the filter’s surface area to optimize particle collection potential. It is also designed to increase the tortuous path of particulate in the filter by maximizing pathways – and does all of this without increasing comparative pressure drop. Mott’s fiber metal medias have differential pressure drop, on par or below those filters made with Teflon medium.

Why is it important to guard against pressure drop? A pressure drop results in a loss of the driving pressure energy. When this occurs, to maintain sufficient flow, technicians must operate vacuum pumps at higher vacuums in point-of-use applications or operate compression pumps at higher pressure for bulk gas applications. Most gases at the point of use in the manufacture of semiconductors are exorbitantly expensive, and if excessive gas is used during operation, or if gas remains unused in the cylinder, it’s a wasted expense. In addition, because some gases are created from a liquid phase and operate  at very low vapor pressure, they are extremely sensitive to pressure drop.  If the vapor delivery system provides too high a pressure drop, the subsequent drop in temperature will allow the vapor to change phase.  Adding heat to the systems can help reduce this temperature drop but using a filter with a minimal pressure drop can reduce the amount of heat required. Mott’s metal filters can withstand temperatures up to 450°C.

Rely on Us to Be A Partner in your Success

Mott’s engineering team is eager to custom design a filter for your application that is highly effective yet cost efficient. For decades, we have worked with dozens of semiconductor companies around the world and have found that our most productive and successful relationships were formed when customers approached us early in the system design phase.

Our engineers will work with your team to ensure our filters perform precisely the way you expect. We’ve studied particle filtration so extensively that a Mott R&D scientist was responsible for co-authoring the SEMI F38 specification for particle filtration efficiency.

Mott ultra-high purity filters are ideal for use in valve manifold boxes, gas cabinets, tool isolation gas boxes and on-board gas delivery boxes. They are manufactured using 316L stainless steel, nickel or Hastelloy® C-22 – all suited to high purity applications requiring high pressures and high temperatures. In fact, our filters can withstand operating temperatures as high as 450°C.

Let Us Create a Filter to Overcome Your Most Challenging Applications

Mott's full line of metal filters, restrictors, and diffusers can be found in our latest semiconductor products catalog.

If you have a more unique filtration challenge, feel free to schedule a time to talk to our team by sending us an email using the button below.

Contact Mott

By: Kevin McGuffin

Title: Vice President, Mott High Purity Filtration

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