Thin Films Characterization by Ultra Trace Metrology

Sensitive and accurate characterization of thin films used in nanoelectronics, thinner than a few nm, represents a challenge for many conventional methods, especially when considering in-line control. With capabilities in the E10 at/cm² (<1/10 000 of a mono layer), methods usually dedicated to contamination analysis appear promising, especially TXRF thanks to its non invasive and ease of use aspects, and to its measurement speed and mapping capability. This study shows that the range of linear results from TXRF can be extended to thicknesses of a few nm when using an incident angle higher than the critical angle of the analyzed film. Thus, despite degraded performances in terms of low detection limit, TXRF can provide a direct and very sensitive reading of some critical deposition processes. A dynamic repeatability better than 1% (standard deviation) has been obtained for the control of a 0.6 nm Al₂O₃ tunnel oxide deposited on a magnetic stack. On the other hand, composition analysis by TXRF, and especially the detection of minor elements into thin films, requires the use of a specific incident angle to optimize sensitivity. Under the best conditions, determination of the composition of Co -based self aligned barriers (CoWP and CoWMoPB films with Co concentration >80%) is done with a precision of 6% on P, 8% on Mo and 13% on W (standard deviation).