ACM Research Shanghai, Ltd. (ACM Research), a subsidiary of ACM Research, Inc., has introduced a new Ultra C 12-inch, single-wafer megasonic cleaning tool for the advanced cleans at 65 nm and below technology nodes at SEMICON China. The new technology enables to tightly and uniformly control megasonic energy distribution across the wafer, allowing particle removal efficiency (PRE) up to 99.2% without damaging the patterned wafer.

Below 65 nm, the gate and capacitor structures become increasingly delicate. As device features become smaller, the critical particle diameter also becomes smaller and more difficult to clean. The danger of the 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,” said David Wang, founder and chief executive officer, 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% using a diluted SC1 cleaning chemical, and 98.3% using de-ionized water only.”

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

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

As the process window for attaining a high PRE without causing damage is so narrow, it is critical to have excellent uniformity of the energy distribution across the whole 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 of 1000 atmosphere, microjet with temperatures of up to 4000 degrees Celsius that can easily damage fragile structures on the wafer.

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

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