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Identification of the Break-In Mechanism by Asperity Deformation of CMP Pad
정경우(Kyeongwoo Jeong),정선호(Seonho Jeong),신소민(Somin Shin),최진욱(Jinuk Choi),정해도(Haedo Jeong) Korean Society for Precision Engineering 2021 한국정밀공학회지 Vol.38 No.2
Chemical Mechanical Planarization (CMP) is an essential process for flattening the surface of the wafer to produce a fine structure. The CMP process is performed after a break-in step prior to optimizing the polishing pad. Break-in consists of the conditioning step and warming-up step. In the conditioning step, a conditioner embedded with diamonds is used to remove residues from the pad surface and manages the directionality and height deviation of asperities on the surface. The warming-up step serves to increase the temperature of the pad surface by polishing multiple wafers. The temperature in the warming-up step is raised due to friction between the wafer and pad, and the pad state is divided into a partly warmed up section, a transition section, and a fully warmed up section of the pad. In this study, as the wafer pressure increased in the warm-up stage, the time for the pad to reach the stable section was confirmed, and the break-in mechanism was analyzed in terms of surface characteristics and mechanical properties, such as surface photograph, surface roughness of the pad, and elastic modulus of pad asperities. Based on these results, the break-in mechanism that increases the material removal rate was analyzed.
Variation of Pad Temperature Distribution by Slurry Supply Conditions
최진욱(Jinuk Choi),정선호(Seonho Jeong),정경우(Kyeongwoo Jeong),정해도(Haedo Jeong) Korean Society for Precision Engineering 2020 한국정밀공학회지 Vol.37 No.12
Chemical mechanical planarization (CMP) is a wafer planarization process that uses chemical reactions initiated by slurry and mechanical actions by pad asperity. The progression of CMP causes temperature deviation on the pad surface. Increase in process temperature results in increased material removal rate (MRR). So, pad temperature distribution is closely related to With-In Wafer Non-Uniformity (WIWNU). In this study, the pad temperature distribution is modelled from the energy perspective and slurry supply location is suggested to reduce temperature deviation. An energy supplying expression was created by setting the micro area and substituting the applied pressure, relative velocity, and process time. The energy and temperature distributions were observed as quite consistent and the temperature peak matched well with highest friction heat point (HFHP). Based on the model expression, the slurry injection position was set to the center of pad, the HFHP and wafer center, and change in temperature distribution was measured. A comparative analysis was carried out employing the existing method that uses multiple nozzles rather than single nozzles and the deviation was reduced by about 18.5% when slurry was supplied to the HFHP for a single nozzle and by 24.7% when the largest flow rate was supplied for multiple nozzles.
Planarization Modeling for Device Pattern with Geometric Characteristics of Pad Asperity
신소민(Somin Shin),이다솔(Dasol Lee),정선호(Seonho Jeong),정경우(Kyeongwoo Jeong),최진욱(Jinuk Choi),정해도(Haedo Jeong) Korean Society for Precision Engineering 2020 한국정밀공학회지 Vol.37 No.8
Chemical mechanical planarization (CMP) is a semiconductor process which is necessary for multi-layer interconnection structure. CMP pad is a consumable used in the process and with numerous asperities on the surface that wear out by the load applied from the contact with the wafer. Also, it has a patterned wafer, the step height is gradually removed by contact of the asperities with upper and lower layers. The contact state would be different according to the step height reduction. Likewise, depending on the pattern size at the specific step height, the maximum radius of the asperity curvature differs whether it reaches the down area. In this study, the height distribution of asperities was expressed as a function of time and asperity height taking into account the wear of asperities, and based on the Greenwood-Williamson theory, a mathematical model for material removal rate considering pattern size was derived. The consistency of the novel model is verified with the CMP experiment conducted using oxide patterned wafers, and the experimental data were compared with the residual step height using theoretical removal rate. The root mean square error of the step height reduction was 19.84 nm.