Study on Chemical-Mechanical Polishing in the Copper Damascene Process
Dr. Ming-Shiann Fen
Dr. Ming-Shih Tsai
研究生：陳辰靜 指導教授 : 馮明憲 博士
在銅鑲嵌式製程研究中，我們做了一詳細的闡述。在實驗一開始，溝渠（trench）外的階層（step）必須先磨除掉，所以選擇對銅有一高移除率的研磨條件，而且有必要選擇一具有較大硬度、較小可壓縮性的研磨墊，如Rodel IC1400? 研磨墊，來避免較低的區域(low features)也被磨到，導致無法達到平坦化的目的。而當溝渠外的銅膜快被移除完時，我們選擇一低的銅移除速率，銅對鉭有高移除選擇比的條件，來完成溝渠外銅完全移除的的步驟。進入到第二步驟，即面臨到鉭、銅、氧化矽介電層移除的選擇比率問題。鑲嵌式製程結果的好與壞就決定在第二步驟中，如何選擇銅對鉭與氧化矽的移除選擇比。我們以氧化矽膠體（colloidal silica）與雙氧水混合的研磨液應用在此步驟，也以鉭與氧化矽的移除率比銅快為研磨條件，有助於降低原本在第一步驟就已造成的碟陷（dishing）現象。而且在過研磨（over-polish）的階段，得到碟陷現象更小的研磨結果。|
Study on Chemical-Mechanical Polishing in the Copper Damascene Process Student: Cheng-Ging Chen Advisor: Dr. Ming-Shiann Feng Dr. Ming-Shih Tsai Institute of Materials Science and Engineering National Chiao-Tung University Abstract Under intensive investigation for Ultra-Large-Scale-Integration (ULSI), copper has emerged as an attractive, alternative choice for future interconnect applications owing to its low electrical resistivity and high electromigration resistance. On the manufacturing of multi-level metallization, globe planarization is one of the crucial techniques. Chemical mechanical polishing (CMP) is the only way known to achieve to the globe planarization. In this thesis, the characterization of abrasives for copper chemical mechanical polishing and the damascene process for Cu metallization are presented. In the study of chemical-mechanical polishing, the removal performances of Cu polished with various alumina abrasives and slurry formulations were investigated. While polishing copper film with various alumina abrasives separately in the DI water and 10 vol.% hydrogen peroxide solution, it is found that the polishing performances are poor, not only low removal rate, but also more than 15% removal non-uniformity. However, mixing the citric acid within the hydrogen peroxide solution, the polishing rate increases because of the dissolution of copper oxide by the citric acid and mechanical abrasion supplied by abrasives. Polishing copper with pure alpha alumina, in the slurry formulation of 10 vol.% H2O2/Citric acid obtained the highest removal rate and the smallest surface roughness, it is indicated that there is a balance between chemical dissolution and mechanical wear during polishing process such that an optimized performance is acquired. In the nitric acid-based slurries, with both H+ and NO3- present, it provides a corrosion environment for copper. The polishing results varied with the characteristics of alumina abrasives. Alternatively, with Benzotriazole (BTA) and citric acid presented in HNO3 based slurry, the behavior of abrasives during polishing would become diverse. The roles of these two additives play to form a native or nonnative passivation film on copper surface to inhibit the corrosion from HNO3, the differences of Cu removal with various abrasives become unapparent. Copper removal is conducted by formation and polishing removal the passivation layers; mechanical abrasion by abrasives was limited. Conclusions in this part are as the following: In the corrosion, e.g., the hydrogen peroxide solution mixed with citric acid or nitric acid-based slurries, no steady CuO forms, copper removal is enhanced with the increased alpha-phase content, density, and primary particle size, and the reduced of the BET surface area of the abrasives. Nevertheless, in the neutral solution or corrosion-inhibited environment, the abrasive behavior is no longer the same as described in the corrosion case. On the topic of Cu-damascene process, the detail procedures during CMP process were investigated. Topography planarization, end-point detection in the first step, and the removal selectivity between copper, tantalum, and silicon dioxide in the second step are discussed. During planarization of the topography of patterned wafer, phase 1 of the first step, high copper removal rate and hard polishing pad instead of soft pad were selected to eliminate topography efficiently. The deformation of pad under load is the most concern about whether the planarization could be achieved. Faster step height reduction occurs on the narrow space region in phase 1 of the first step. In order to release the process window for end-point detection, low copper removal rate and high removal selectivity of Cu to Ta would be required and carried out by polishing with optimized slurry formulation in the phase 2 of the first step. For the second step, the key issue is to find a slurry formulation with appropriate suitable removal selectivity of Cu/Ta/Oxide. The removal selectivities of Cu/Ta/Ox are 1: 3.7: 1.63 for slurry pH 7, and 1: 5.76: 2.76 for slurry pH 8. Copper dishing and oxide erosion were evaluated. Copper dishing resulted in the first step was reducing after the second step of damascene process and the amount of dishing for each measured linewidth was less than 1000 A. Oxide erosion was about less than 1000A for low pattern density region, but more than 1200 A for high pattern density region.
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