Proprietary SAPS Megasonic Technology Delivers Damage-Free, High Particle Removal Efficiency

Semiconductor Equipment startup ACM Research Shanghai, Ltd., today unveiled at SEMICON China the Ultra C™ 12-inch, single-wafer megasonic cleaning tool for advanced cleans at the 65 nm and below technology nodes. ACM's proprietary technology allows it to tightly and uniformly control the megasonic energy distribution across the wafer (2% at 1s), enabling particle removal efficiency (PRE) up to 99.2 percent without damaging the patterned wafer.

One of the biggest challenges in semiconductor cleaning technology today is managing mechanical damage and defect levels as the industry moves to smaller device nodes. Below 65 nm, gate and capacitor structures become increasingly fragile. As device features become smaller, the critical particle diameter also becomes smaller and more difficult to clean. The danger of structural damage to downscaling features has become a major issue, resulting in a process window that continuously shrinks.

“Although megasonic cleaning is touted by the industry as the long-term solution for many of the most critical cleaning challenges, no company to date has been able to control the mechanical process window,” stated David Wang, Founder and CEO, ACM Research. “Our Ultra C cleaner is the industry’s first to control the megasonic power and uniformity well enough to deliver damage-free cleaning with PRE over 99.2 percent using a diluted SC1 cleaning chemical, and 98.3 percent using de-ionized water only.”

ACM’s proprietary Space Alternated Phase Shift (SAPS) megasonic technology, which enables highly uniform megasonic power density within wafer (WIW) and wafer-to-wafer (WTW) non-uniformity of less than 2 percent, compared to 10-20 percent non-uniformity offered by other single wafer megasonic cleaning tools currently on the market.

Megasonic power is effective because the process causes cavitation (the formation of bubbles), which helps remove particles and bring them to the surface. The key is to control the mechanical process window of the megasonic energy so that there is enough energy to cause cavitation, but not so much that it causes damage to a patterned wafer.

Because the process window for achieving a high PRE without causing damage is so narrow, it is critical to have excellent uniformity of energy distribution across the entire wafer. When megasonic power is not uniformly distributed, ‘hot spots’ form on the wafer where megasonic energy is higher, causing bubbles to collapse. When a megasonic bubble collapses, it releases a high-pressure (1000 atmosphere) ‘microjet’ with temperatures of up to 4000 degrees Celsius that can easily damage fragile structures on the wafer.

ACM’s SAPS megasonic technology uses a stable cavitation bubble oscillation method, allowing the bubbles to continuously inflate and deflate without collapsing. SAPS enables damage-free megasonic cleaning with ultra-uniform energy distribution (2% at 1s) for optimal particle removal efficiencies.

Although ACM has demonstrated 98.3 percent PRE rates with De-Ionized Water (DIW) alone, the Ultra C offers the flexibility to connect up to five chemicals simultaneously, each with its own customizable separation and reclaim functions.

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