Paper AS-MoA4
ToF-SIMS MCs_x⁺ Dual Beam Depth Profiling with Improved Dynamic Range

Monday, October 29, 2012, 3:00 pm, Room 20

In recent years MCs_x⁺ depth profiling has become increasingly popular for the analysis of thin films using Time-of-Flight SIMS (ToF-SIMS). The MCs_x⁺ mode offers quantitative or semi-quantitative SIMS data and allows for the measurement of electropositive and electronegative elements simultaneously by detecting MCs⁺ and MCs₂⁺, respectively. In addition, the use of heavy cluster ions like Bi₃⁺ or C₆₀⁺ allows for a significant increase of the MCs_x⁺ yields by a factor of up to 1000 with respect to Ga as primary ion projectile and leads to a remarkable improvement of the achievable detection limits [1].

However, one disadvantage of current TOF-SIMS instruments for the quantification in MCs_x⁺ mode is the limited dynamic range, which restricts the possibility of achieving high sensitivity on the MCs_x⁺ clusters and of using the Cs_x⁺ intensity for normalization. The normalization is especially important for the analysis of layer systems where sputter rates or the cesium surface concentration might change from layer to layer. This requires a registration system which is able to detect more than 100 secondary ions of a specific element per primary ion gun pulse with high linearity.

We have developed a new registration system for TOF-SIMS, which increases the useable dynamic range by a factor of 100 i. e. 1E7 counts/sec with an excellent linearity. In addition, the maximum pulsed primary ion current of the bismuth liquid metal ion gun was increased in order to further improve the detection limits for low concentration elements. In this paper we will discuss the characteristics of this new experimental setup and the benefits for the quantitative depth profiling in the MCs⁺ mode.

[1] E. Niehuis, T. Grehl, F. Kollmer, R. Moellers, D. Rading, SIMS Europe, Muenster, 2006