Quantitative measurement of the moisture content in thin films

A description is given of the modification and application of a moisture evolution analyzer to quantitatively measure the moisture content of thin-film dielectrics used in VLSI manufacture. The development of computerized acquisition of moisture, temperature, and time data permits adsorbed water to be distinguished from more tightly bound absorbed water. The incorporation of a computer-driven temperature controller and a 7-in.-diameter crucible furnace allows the moisture evolution characteristics of thin films on 150-mm-diameter wafers to be studied under a wide variety of temperature cycles and ramps up to 1000°C. Studies of thermal oxides, plasma oxides, spin-on-glass, and CVD doped and undoped oxides show moisture contents from less than 0.01 wt.% to in excess of 10 wt.% water, demonstrating the sensitivity and range of the technique. The results for borophosphosilicate glass (BPSG) thin films as a function of doping levels are presented. The moisture in these films was found to be partitioned approximately equally between adsorbed and absorbed moisture. As the doping levels (wt.%B/wt.%P) were varied from 0/4.2 to 2.5/3.8, the moisture content varied by 30%. The effects of low-temperature heat treatments and alternative deposition chemistries are also discussed