EFFLUENT MONITORING WITH FTIR SPECTROSCOPY FOR LOW OPEN AREA OXIDE ETCH ENDPOINT DETECTION

摘要

We used Fourier transform infrared (FTIR) spectroscopy to monitor the effluent exhausted from an Applied Materials 5300 high density plasma reactor where C_2F_6 was used for contact etch. A variable pathlength gas cell sampled effluent between the turbo and roughing pumps. Patterned wafers with variable oxide thickness and exposed area, blanket resist wafers and dummy wafers (thick oxide with 1% open area but no expected endpoint) were used. When etch endpoint occurred, several species exhibited a change in absorption intensity, which is especially true for the larger open area wafers. In particular, C_2F_6 and C_2F_4 showed an apparent rising signal as the oxide film started to clear. By tracking C_2F_4 or C_2F_4 intensity, endpoint was clearly identified. The time of endpoint occurrence increased consistently with increasing the oxide thickness. No endpoint signature was observed for blanket resist and dummy wafers. In order to amplify the small endpoint signal from low open area wafers, absorption intensities of more than one species were tracked throughout the main etch process. A broad spectral range was. processed using Evolving Window Factor Analysis. This statistical analysis method combined with FTIR improved the quality of endpoint determination for low open area wafers.