Carrier illumination for characterization of ultrashallow doping profiles

Abstract

Depth profiling of ultrashallow B implants in silicon using a magnetic-sector secondary ion mass spectrometry instrument J.The Carrier Illumination™ ͑CI͒ method is an optical technique for nondestructive in-line monitoring of postanneal junction depth, preanneal preamorphization implant depth, and dose. This work intends to extend the use of the CI measurements from a relatively process specific quantitative measurement towards a more universal quantitative analysis of junction depth, profile abruptness, and implant dose. For that purpose the predictive capabilities of the present physical models with respect to the quantitative dependence of the CI signal on the applied generation power is investigated for a wide variety of samples, including bulk material, highly abrupt chemical vapor deposition grown ͑B͒ structures, and implanted ultrashallow junctions ͑B, BF 2 , As͒. In general, the CI signal may arise from a combination of three components: a primary one originating from the reflection of the probe laser beam from the dopant profile depth corresponding with the injected excess carrier level, in some cases, from reflection from near-surface carriers, and in other cases, from residual damage within the doped region.

Extracting active dopant profile information from carrier illumination power curves

“…It has been reported in previous work 6 that the CI signal correlates with junction depth following a cosine-like behavior of 68 nm half-wavelength ͑980/ 4n lat ͒ where the highly doped samples are shifted downwards relative to the lowly doped samples ͓Fig. 1͑a͔͒.…”

Progress in the physical modeling of carrier illumination

“…Consequently, negative CI signals are found, for example, on a 5 ϫ 10 19 cm −3 homogeneous wafer, opposite to what is believed until now. 27 The scattering of the experimental points at low doping concentrations is believed to be due to uncertainties in the SRH lifetimes which are known to be degraded during a natural light exposure because of the formation of BO n complexes. 28 Let us now focus on highly doped ͑10 17 -5ϫ 10 20 cm −3 ͒ p-type sub-100-nm box profiles on lowly doped p substrates ͑10 15 cm −3 ͒.…”

Towards nondestructive carrier depth profiling

“…8 Hence, the quadrature signal on CVD structures can apparently be modeled in a similar way, i.e., as the interference between a surface reflection ͑proportional to the surface plasma density N surf ͒ and the reflection at the internal CVD-substrate interface ͑proportional to the difference in plasma density in the surface layer and the substrate N sub ͒, based on formula ͑1͒. 1͑b͔͒.…”

“…Earlier work has illustrated that in the quasistatic mode ͑also referred to as carrier illumination 8 ͒ it is possible to extract junction depths on ultrashallow box profiles ͓i.e., chemical vapor deposited ͑CVD͒ grown layers͔ with subnanometer depth resolutions, provided one knows in advance the corresponding peak carrier concentration level. Earlier work has illustrated that in the quasistatic mode ͑also referred to as carrier illumination 8 ͒ it is possible to extract junction depths on ultrashallow box profiles ͓i.e., chemical vapor deposited ͑CVD͒ grown layers͔ with subnanometer depth resolutions, provided one knows in advance the corresponding peak carrier concentration level.…”