W. De Coster

RBS, AES and XPS analysis of ion beam induced nitridation of Si and SiGe alloys

Abstract Nitridation of Si and SiGe alloys under normal incidence 12 keV N + 2 bombardment has been studied by in situ 1 MeV 4 He RBS and by ex situ XPS and AES analysis. The in situ RBS measurements, which alternate with the sputtering/bombardment cycles, show the build-up of the nitrogen content in the silicon and Si .86 Ge .14 sample with increasing N + 2 dose. For the silicon a stoichiometric ratio close to that of Si 3 N 4 is found. In the case of the SiGe alloy a depletion of the Ge from the surface is noticed. Ex situ XPS measurements on the same samples indicate that nitrogen is bonded with silicon and germanium according to the Si 3 N 4 and Ge 3 N 4 phase. AES analysis of the steady state composition gives a depth profile with qualitative information on the chemical binding. Nitridation of a silicon sample with a buried Ge layer demonstrates that during the nitrogen build-up a large densification and even some swelling of the surface layer occurs. The transient region of nitridation before steady state is reached is explained by a two-phase model.

Ion beam mixing and oxidation of a Si/Ge-multilayer under oxygen bombardment

Abstract In many commonly used physical analysis techniques in semiconductor industry, low energy ion bombardment is used for material removal in depth profiling. To know how the irradiation influences the material to be investigated, it is necessary to gain insight in the processes taking place during the interaction of the ion with the substrate. Silicon samples with a buried Ge-layer as a marker have been bombarded with 12 keV O2+ at different angles of incidence and analysed with in situ RBS. While under normal incidence a well-defined SiO2-layer with sharp interfaces is formed, for angles from normal incidence the oxygen incorporation decreases and Si-suboxides are seen by ex situ XPS. During oxygen bombardment, when the silicon overlayer is converted to an oxide-layer, Ge migrates towards the surface before the sputter front has reached the Si/Ge-interface. On the other hand, in the dilute limit Ge-segregation to the interface is noticed under normal incidence.

Depth profiling of light-Z elements with elastic resonances: Oxygen profiling with the 3.045 MeV 16O(α, α)16O resonance

Abstract Depth profiling of light elements in high-Z substrates can be done with RBS using elastic resonances. With the resonant signal in the backscattered spectrum several parameters can be associated as such as height, position, yield and FWHM. The dependence of the parameters on incident beam energy will be described. The influence of the energy spread and of the detector resolution, which limits the use and accuracy, is discussed. Computer calculations are given to establish the validity of the model and to illutrate the restrictions. A methodology which uses the different parameters is proposed. Experimental results are shown for the depth profiling of oxygen in 20 nm, 89 nm and 500 nm thick oxides with the elastic 3.045 MeV 16 O ( α , α ) 16 O resonance.

Stoichiometry changes during low energy oxygen bombardment

Abstract A basic understanding of the sputter induced artifacts during low energy oxygen ion beam bombardment is of great importance for a correct evaluation of the results of suptter depth profiling in SIMS. In this paper the sputter depth profiling of Si, CoSi2 and TiSi2 under normal oxygen bombardment has been investigated. With the combined sputter/RBS set-up and in combination with ex-situ XPS measurements, the oxidation and near-surface compositional changes in the transient region have been explained.

In situ observation by RBS of oxygen gettering during Cs sputtering of Si-based materials

Abstract In SIMS, Cs is commonly used as the bombarding species to enhance the yield of negative secondary ions. Using RBS we have studied the incorporation of Cs in Si-based materials in order to understand the Cs build-up and surface modification during SIMS analysis. It is shown that Cs at the surface acts as a getter for oxygen from the residual gas resulting in the oxidation of the altered layer. Increasing the incident angle from normal incidence to 40° suppresses the gettering and oxidation by the higher erosion rate. In SiGe-alloys the gettered oxygen causes preferential oxidation of Si with respect to Ge, leading to the pile-up of Ge at the back of the oxide.

In situ RBS analysis of ion beam mixing during low energy sputtering

Abstract Low energy ion sputtering for depth profiling in SIMS, AES and XPS produces sputter induced artifacts. These effects are studied by comparing RBS spectra of the bombarded layer to the original target composition. For this purpose an automated RBS chamber has been built combining an Atomika SIMS system and a NEC microprobe RBS beam line. In this article the effect of ion beam mixing of Pt on Si and of CoSi 2 on Si under oxygen bombardment, as well as the preferential sputtering of Si in CoSi 2 under Ar bombardment are demonstrated.

Various advanced capabilities of the RBS setup at IMEC

Abstract This article describes the various capabilities of the ion-beam analysis facility at IMEC which is designed to fulfill two needs. One is the high volume analysis service of material originating from the processing and material development groups at IMEC and the other is the research associated with gaining improved insight in the different analysis methods used for semiconductors, in particular all the aspects related with ion sputtering, and the development of improved analysis capabilities in order to cope with the demands from the analysis service. The latter includes the incorporation of a TOF spectrometer for heavy-ion RBS and ERD, the investigation towards the application of heavy-ion RBS for improved sensitivity, the application of angle resolved image scans for fast and certified channeling analysis and resonant analysis by automated energy scanning.

Heavy-ion irradiation effects on passivated implanted planar silicon detectors

Abstract Commercially available p+nn+ passivated implanted planar silicon detectors have been shown to be very performing for standard RBS-analysis with 4He beams. Lifetimes are found to range up till > 109 particles. The end of lifetime occurs concurrent with internal breakdown of the detector. Inverted n+ np+ detectors where the junction is located well outside the damage region, are expected to be less sensitive to the radiation damage and to have a higher lifetime. In the present paper the characteristics for heavy-ion detection of both types of detector are investigated and discussed upon.

Sputtering phenomena of CoSi2 under low energy oxygen bombardment

Sputter depth profiling with AES, XPS and SIMS suffers from sputter induced artifacts such as preferential sputtering, segregation phenomena and recoil displacements. A combined in situ sputter RBS system has been used to study the sputter process into detail. In this work the beam induced oxidation of CoSi2 during low energy oxygen irradiation is investigated. The oxygen bombardment of CoSi2 offers a very complex behavior as a function of dose where we first observe a gradual Co depletion subsequently followed by a replenishment of this depleted region. Additional XPS and TEM analysis of the bombarded CoSi2 shows that the transient behavior can be correlated with changes in oxidation and different phase formations.

Resonance depth profiling of low-Z elements with target biasing applied to the 3.045 MeV 16O(α, α)16O resonance

Resonance scanning represents an alternative to Rutherford backscattering spectrometry for the quantitative depth profiling of light elements in high-Z substrates. An alternative to automatic energy scanning devices, which are based on “fooling” the slit-control system, is presented. For the actual energy variation the target biasing technique is used. The principles are described as well as some intrinsic restrictions to this technique. Tilting the target to increase the depth resolution is impeded by the influence of the electrical field gradients under glancing incidence conditions. Under these glancing angles the beam is influenced by the target potential. The target biasing technique is applied to the resonance oxygen probing in oxide layers with the 3.045 MeV 16O(α,α)16O resonance.