M. F. C. Willemsen

Hydrogen in low‐pressure chemical‐vapor‐deposited silicon (oxy)nitride films

Silicon (oxy)nitride films (SiOxNy) have been deposited onto silicon by low‐pressure chemical vapor deposition using SiH2Cl2, N2O and NH3 or ND3. Nuclear reaction analysis, elastic recoil detection, and Rutherford backscattering spectrometry have been used to determine the elemental composition of the films with emphasis on the hydrogen and deuterium content. In the as‐deposited, NH3‐grown films the bulk hydrogen concentration is about 3 at. % for an oxygen/nitrogen atomic ratio (O/N) smaller than 0.4, for O/N>0.4 it is lower. In 900 and 1000 °C vacuum annealed films the bulk hydrogen concentration as a function of O/N goes through a maximum at O/N≊0.4. By comparing this observation with the D content in ND3‐grown films as a function of O/N, a model is deduced which explains this behavior. This model involves an oxygen induced increase of the electronegativity of the atoms to which hydrogen/deuterium is bound. Annealing at 1000 °C in a H2/N2 gas mixture of NH3‐grown films results in bulk hydrogen concentr...

In situ investigation of TiN formation on top of TiSi2

TiN formation on TiSi2 has been studied using in situ Rutherford backscattering spectroscopy and Auger electron spectroscopy. Two systems were investigated: (i) the reaction of Ti with nitrogen and (ii) the nitridation of TiSi2. When a Ti film on Si is annealed in N2 or NH3, two reactions occur simultaneously: TiN forms at the surface and TiSi2 at the interface. Oxygen, dissolved in the original Ti film, is expelled from the growing silicide and is piled up at the TiN/TiSi2 interface. Around 600 °C, the complete conversion of the upper nitrogen‐containing layer into TiN is retarded by this oxygen and a TiNxO1−x layer remains detectable between the TiN and TiSi2 layers. At 750 °C, the TiN layer is formed very rapidly and further growth is blocked by the TiSi2 layer that has developed underneath. Nitridation of TiSi2 requires a temperature of at least 800 °C. Starting at the exposed surface, the silicide layer is gradually converted into TiN. Some of the Si released in this reaction segregates to the surfac...

Hydrogenation during thermal nitridation of silicon dioxide

The incorporation of nitrogen and hydrogen during nitridation of SiO2 was studied over the temperature range of 800–1000 °C and for ammonia pressures of 1, 5, and 10 atm. The nitrogen content of the nitrided films was determined with Rutherford‐backscattering spectrometry and elastic‐recoil detection. Nitrogen in‐depth profiles were obtained applying Auger analysis combined with ion sputtering. Hydrogen profiles in the films were measured using nuclear‐reaction analysis. Both the nitrogen and hydrogen incorporation were found to increase with temperature in this range. A higher ammonia pressure primarily increases nitridation of the bulk of the oxide films. Depending on the nitridation conditions, up to 10 at.% of hydrogen may be incorporated. As distinct from the nitrogen profiles, the hydrogen in‐depth profiles are essentially flat. The concentration of hydrogen in the films, however, was always found to be smaller than that of nitrogen: measured H/N ratios varied between 0.25 and 0.85, the smaller valu...

Thermal oxidation of silicon nitride and silicon oxynitride films

The oxidation behavior of low‐pressure chemical vapor deposition silicon oxynitrides was investigated for layer compositions ranging from that of pure nitride to oxynitride with an atomic ratio of O/N=1. Oxidations were performed at 850–1000 °C in ambients having different H2O/O2 flow ratios. Rutherford backscattering spectrometry and elastic recoil detection were employed to quantify the increase in oxygen content of the films upon oxidation. Hydrogen profiles in oxidized samples were measured using nuclear reaction analysis and elastic recoil detection. We observed that the oxidation rate for either oxynitride composition is nearly two orders of magnitude smaller than that of silicon. Linear oxidation kinetics were measured for the conditions applied in this study, which are indicative of a reaction‐controlled process. The activation energy of this process was determined to be 2 eV for silicon nitride and appeared to decrease with growing oxygen content in oxynitrides. The hydrogen profiles measured in ...

Surface segregation and initial oxidation of titanium silicide films

The high‐temperature behavior of TiSi2 films, deposited on a polygate structure, was studied by means of Auger electron spectroscopy and low‐energy ion scattering. Both techniques reveal that upon heating at temperatures in excess of 600 °C the surface of the silicide film becomes Si‐enriched to an extent corresponding to TiSi4. This observation is in qualitative agreement with the theory of surface segregation, which predicts enrichment of the element with the lowest heat of vaporization. However, the effect is found not to be restricted to the topmost atomic layer, but extends to a depth of 30–40 A. With oxygen, introduced into the vacuum system to a level of 10−6–10−4 Torr, the same amount of enrichment is obtained, now at 500–600 °C. In this temperature range Ti desorbs from the silicide as TiOx. Apart from the outer surface layer the silicide is not oxidized under these circumstances. At higher temperatures, around 800 °C, this reactive adsorption–desorption of oxygen does not result in the formation...

Hydrogen profiling by proton-proton scattering

Abstract Proton-proton scattering is used to measure the hydrogen profile in thin films. It is demonstrated that the sensitivity to hydrogen can be improved by using two detectors and detecting the emerging protons in time-coincidence. The effect of the incident beam energy and the exit angles on the sensitivity and depth resolution is measured. Taking an LPCVD Si 3 N 4 layer as an example a detection limit of 0.1 at.% and a depth resolution of 700 A is determined.

Ion implantation and diffusion of Zn in GaAs

Zn implantation (dose 5×1015 cm−2) and subsequent diffusion were carried out on GaAs wafers and on liquid‐phase epitaxial GaAs layers. A silicon nitride cap was deposited by chemical vapor deposition (CVD) or by sputtering either before or after implantation. Profiles were determined with Secondary Ion Mass Spectrometry and Differential Hall Effect measurements and damage was studied with Rutherford Backscattering Spectrometry. Annealing gave rise to Zn segregation at the surface or just below it and at a depth past the implantation maximum. The diffusion was much deeper and the damage recovery was much less with implantation through a nitride layer than with implantation directly into GaAs. This is explained in terms of recoil implantation of Si and N and of a smaller Ga vacancy concentration so that less trapping of interstitial Zn by such vacancies takes place. Surface segregation of Zn and differences in diffusion depth between samples with sputtered and CVD silicon nitride caps are ascribed to the ef...

The effect of ion beam mixing on MoSi2 formation

Thin Mo films on Si were mixed by As * ion bombardment at room temperature. This results in an amorphous intermixed layer of varying composition and, at greater depth, in the amorphization of silicon. The formation of MoSi 2 from these implanted structures by thermal reaction has been studied by glancing angle Rutherford backscattering and in situ annealing. These experiments show that ion beam mixing of the interface disperses the interfacial oxide, which is present between Mo and Si and initially a homogeneous reaction occurs. However, when the amorphized silicon has regrown epitaxially, the reaction becomes inhomogeneous or even stops. The dispersed oxygen is apparently snowploughed in front of the interface of amorphous and crystalline silicon leading to a restoration of the oxide barrier.

Particle-induced X-ray emission of light elements

Abstract With an X-ray detector capable of measuring photons at an energy as low as 300 eV, it is possible to perform PIXE analysis of light elements. In combination with RBS the X-ray production of N, O and F as a function of the incident proton or He-ion energy can be quantified. The possibility of accurate quantitative analysis of low- Z materials is demonstrated. The fluorescence yields of N, O and F, that can be extracted from the measured X-ray production, are found to deviate from theory. The differences can be explained by the effects of chemical binding and multiple ionization on the physical processes involved in the particle-induced X-ray emission.

LPCVD of tungsten studied with in-situ RBS

Abstract The deposition of W on Si from WF 6 at low pressure was studied in a high-vacuum reactor equipped with an in-situ RBS facility. The W deposition was found to stop within 1 or 2 minutes, for all temperatures investigated in the range of 150–600 ° C. The temperature dependence of this self-limiting thickness displays an Arrhenius-type behaviour, corresponding to an apparent activation energy of 0.33 eV. This energy is proposed to be related to Si transport determining the ultimate W film thickness. The deposition of W is accompanied by a 1.5–3 times larger Si consumption, governed by the reaction temperature. Both the occurrence of self-limiting deposition and of Si consumption can be effectively suppressed by adding H 2 to the reactor at a partial pressure ratio exceeding H 2 WF 6 = 10 .