In Situ Temperature Measurement During Oxide Chemical Mechanical Planarization
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In Situ Temperature Measurement During Oxide Chemical Mechanical Planarization Jesse Cornely1, Chris Rogers1, Vincent Manno1 and Ara Philipossian2 Tufts University, Department of Mechanical Engineering Medford, MA 02155, U.S.A 2 University of Arizona, Department of Chemical Engineering Tucson, AZ 85721, U.S.A 1
ABSTRACT This paper presents temperature and friction force data at the pad-slurry-wafer interface during real time CMP polishing with in situ pad conditioning. Experiments are performed on a 1:2 scale laboratory tabletop rotary polisher with variable pad speed and wafer down force control. Dual emission laser induced fluorescence (DELIF) techniques are used to optically measure the temperature directly beneath the wafer during polishing using a two camera imaging system. An infrared camera and a thermocouple are alternately used to measure bow wave temperatures. Optically transparent BK-7 glass wafers with either concave (wafer edges sloping toward the pad) or convex (wafer edges sloping away from the pad) curvature were used. When concave wafers are polished, the bow wave temperatures are 3°C to 5°C higher than the corresponding value for convex wafers. Similarly, slurry temperatures under the concave wafers are 5°C to 6°C higher than the value for convex wafers (±0.5°C). The friction force per unit area is typically 2 kPa to 3 kPa higher for concave wafers. Temperatures beneath the wafer are as high as 12°C above the ambient temperature for a concave wafer at a high applied wafer pressure (41.4 kPa) or linear velocity (0.93 m/sec). Bow wave temperatures reach as high as 9°C above ambient at a linear velocity of 0.93 m/sec. The lowest temperatures, within 1°C of ambient at the bow wave and 5°C above ambient under the wafer, were found with convex wafers at low applied wafer pressures (20.7 kPa). Linear velocity has little effect on the slurry temperature while polishing convex wafers. Increasing slurry abrasive concentration causes an increase in temperature, despite a decrease in friction force. A correlation, with an R-squared value greater than 0.96, exists between the bow wave temperature and the temperature beneath the wafer. This correlation holds at constant linear velocities across wafer shapes, applied wafer pressures, and slurry concentrations. INTRODUCTION Temperature is an important parameter in the chemical mechanical polishing (CMP) process. The slurry-wafer interface temperature can influence the rate of chemical reactions, thus affecting the rate of material removal. Temperature affects the surface and bulk characteristics of the polishing pad. Pad temperature is also a reliable indicator of performance metrics, such as pad degradation, polish endpoint, and wafer uniformity. While the pad temperature is fairly easy to measure, there is great difficulty in measuring the temperature at the pad-slurry-wafer interface. The constantly moving parts and extremely thin gap between the pad and wafer make it difficult to insert probes. There is an increasing need to have the ability to measur
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