SiO2 thickness determination by x-ray photoelectron spectroscopy, Auger electron spectroscopy, secondary ion mass spectrometry, Rutherford backscattering, transmission electron microscopy, and ellipsometry

As the R-p of ion implants steadily decreases an ever-increasing percentage of the implant species lies in the oxide layer and is, therefore, not elec trically active. For this reason, it is important to have analytical techni ques capable of accurately measuring the thickness of ultrathin oxide layer s. A round-robin study was performed on a series of SiO2 films ranging from 0.3 to 20 nm in order to evaluate the advantages and disadvantages of five commonly used analytical techniques. High-resolution cross-section transmi ssion electron microscopy (TEM) offers the only true measurement of oxide t hickness because no density assumptions are made. In this study, TEM is use d as the standard for all the other techniques. X-ray photoelectron spectro scopy and Auger electron spectroscopy offer precise measurements for ultrat hin (<3 nm) films, but are limited for thicker films (>15 nm) due to the ex ponential decay functions that describe the sampling depth in both techniqu es. Secondary ion mass spectrometry (SIMS) has historically been used for c haracterizing relatively thick films (>10 nm) but not for thinner films bec ause of atomic mixing effects. Encapsulating oxides with amorphous silicon prior to performing a SIMS experiment can negate these effects. A compariso n of SIMS on encapsulated and as received films is made. Rutherford backsca ttering is an excellent technique for determining oxide thickness over a wi de thickness range by channeling the Si signal from the crystalline substra te and analyzing oxygen from the amorphous oxide. Ellipsometry, being both rapid and low cost, is one of the most widely used techniques capable of ac curate measurements on thick films (>10 nm). (C) 2000 American Vacuum Socie ty. [S0734-211X(00)08401-8].