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Post-CMP Clean PVA Brush Design Advancements and ...

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International Conference on Planarization/<strong>CMP</strong> Technology · October 25 – 27, 2007 Dresden<br />

VDE VERLAG GMBH · Berlin-Offenbach<br />

clean brush design (chemically, mechanically, <strong>and</strong> dimensionally), <strong>and</strong> methods of tribological <strong>and</strong><br />

P<strong>CMP</strong> cleaning evaluations to ensure consistent frictional characteristics as well as wafer cleaning<br />

performance, throughout the brush lifetime. This study also demonstrates the benefits of using MTTC<br />

design <strong>PVA</strong> brushes in Cu/low-k P<strong>CMP</strong> cleaning applications.<br />

2. <strong>Post</strong>-<strong>CMP</strong> <strong>Clean</strong>ing Process Characteristics<br />

<strong>CMP</strong> processes use abrasive slurries in the planarization process. After <strong>CMP</strong>, the wafers need to be<br />

cleaned to remove the slurry abrasive, organic residues <strong>and</strong> other particles. This P<strong>CMP</strong> cleaning is<br />

accomplished employing different tools <strong>and</strong> P<strong>CMP</strong> clean chemistries. Advanced <strong>CMP</strong> tools have<br />

integrated P<strong>CMP</strong> modules, enabling wafer cleaning cycle to be dry in <strong>and</strong> dry out to prevent<br />

contamination. The P<strong>CMP</strong> cleaning chemistry is typically sprayed on top of the brush, with DI water<br />

flowing out through the core. A combination of chemical action (provided by cleaning chemistry) <strong>and</strong><br />

mechanical action of the rotating <strong>PVA</strong> brush removes the wafer surface deposits. With NH4OH at pH<br />

~10-11, <strong>PVA</strong> brush, wafer <strong>and</strong> the slurry abrasive particles, all have similar negative zeta potential.<br />

The above results in repulsion between <strong>PVA</strong> <strong>and</strong> particles, no particles deposit on <strong>PVA</strong>, <strong>and</strong> no<br />

scratches. An efficient post-copper <strong>CMP</strong> cleaning operation should remove particles, organic residues,<br />

<strong>and</strong> ionic contamination, control the copper corrosion, prevent water marks on dielectric <strong>and</strong> leave the<br />

polished surface free from all contamination <strong>and</strong> defects, providing an acceptable process throughput<br />

<strong>and</strong> cost of ownership. <strong>Clean</strong>ing performance of <strong>PVA</strong> brush strongly depends on the chemical <strong>and</strong><br />

mechanical properties <strong>and</strong> stability of the brush material, magnitude of wafer-brush frictional force,<br />

<strong>and</strong> adhesion forces between the particle <strong>and</strong> wafer as well as the particle <strong>and</strong> brush. Zeta potentials of<br />

the particle <strong>and</strong> the wafer in various cleaning solutions <strong>and</strong> pH of the <strong>CMP</strong> slurry are very important in<br />

the particle adhesion <strong>and</strong> removal in post-<strong>CMP</strong> clean process. Comparative frictional attributes as<br />

determined by wafer-liquid-brush interface coefficient of friction (COF), <strong>and</strong> mechanical integrity in<br />

terms of contact-pressure <strong>and</strong> contact-area can provide valuable insights on the lubricious behavior of<br />

wafer-brush contact <strong>and</strong> brush lifetime. <strong>Post</strong>-<strong>CMP</strong> cleans may range from extremely acidic: pH11(e.g., TMAH based) <strong>and</strong><br />

may contain surfactants <strong>and</strong> chelating agents.<br />

3. Common <strong>Post</strong>-<strong>CMP</strong> <strong>Clean</strong>ing Technologies<br />

Megasonic <strong>and</strong> Double Sided <strong>Brush</strong> Scrubbing - Slip-on-the-core (SOTC) <strong>and</strong> Molded-through-thecore<br />

(MTTC) <strong>PVA</strong> <strong>Brush</strong> <strong>Design</strong>s<br />

A st<strong>and</strong>ard, hollow cylindrical<br />

sponge with nodules<br />

Double Side <strong>Brush</strong> Scrubbing<br />

Molded-through-the-core <strong>Design</strong> <strong>PVA</strong> <strong>Brush</strong><br />

(Planarcore)<br />

Megasonic <strong>Clean</strong>ing<br />

Slip-on-the-core <strong>Design</strong> <strong>PVA</strong> <strong>Brush</strong><br />

4. Planarcore <strong>PVA</strong> <strong>Brush</strong> <strong>Design</strong> for <strong>Post</strong>-<strong>CMP</strong> <strong>Clean</strong>ing Applications<br />

<strong>PVA</strong> brushes used to be an industrial product before being introduced at IBM <strong>and</strong> commercialized in<br />

the early 1990’s. Entegris molded-through-the-core (MTTC) design is a disposable <strong>PVA</strong> brush that<br />

reduces tool downtime <strong>and</strong> provides excellent dimensional stability over its lifetime. MTTC design<br />

provides positive anchoring of <strong>PVA</strong> to the core <strong>and</strong> eliminates possibility of any slippage at the <strong>PVA</strong>-

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