AVS 58th Annual International Symposium and Exhibition
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThP

Paper PS-ThP25
Development of Inductively Coupled Hydrogen Plasma Source with a Ceramic Tube

Thursday, November 3, 2011, 6:00 pm, Room East Exhibit Hall

Session: Plasma Science and Technology Poster Session
Presenter: Janghwee Cho, PSK Inc., Republic of Korea
Authors: J. Cho, PSK Inc., Republic of Korea
J. Yang, PSK Inc., Republic of Korea
S. Park, Inha University, Republic of Korea
D. Lee, Inha University, Republic of Korea
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Organic photoresist in semiconductor photolithographic process has been removed by downstream oxygen plasma which is generated in a quartz chamber or tube. In case of stripping heavily ion-implanted photoresist whose surface is carbonized by energetic ions, it is sometimes necessary to add CF4 gas to oxygen. Moreover, hydrogen based plasma begins to be used to strip photoresist coated on low-k dielectric layers, where oxygen plasma is known to degrade low-k dielectric films. However, fluorine or hydrogen ions can attack the quartz walls and generate particles. To solve this problem, plasma generation chamber should be made of materials inert to fluorine or hydrogen ions. In this work we have designed and constructed a plasma source chamber made of ceramic tube. A 12 cm diameter ceramic tube is surrounded by a Faraday shield and wound by a 4 turn helical coil connected to 13.56 MHz RF power. There are also two turn dummy coils, which are electrically grounded, at the top and bottom sides of the 4 turn power coil. All coils have hollow square cross-section and cooling water flows through the coils. At the bottom of the 25 cm long tube an electrically grounded baffle with many small holes are located and only radicals are fed to the stripping process chamber for 300 mm wafers. Because ceramic materials usually have larger thermal expansion coefficient than quartz, larger thermal stress exists in the ceramic tube across tube thickness and at gaps between cooling coils, which results in breakage of ceramic tube. It is very important to achieve good thermal contacts between cooling water coils and tube wall and thus small temperature gradient in the tube. We have investigated the temperature profiles and thermal stress to the ceramic tube in terms of ceramic tube materials (Al2O3 and AlN), types of ceramic paste to glue cooling coils to the ceramic tube, size of cooling coils, thickness of ceramic tube, and RF impedance matching methods. It is found that AlN which has larger thermal conductivity than Al2O3 shows no breakage of tube. Size of cooling coils and types of ceramic paste have no effect on tube breakage. In case of Al2O3, thinner tube survives from breakage. It is confirmed that little side wall attack is observed after 1000 runs of photoresist strip by H2/N2 plasma.