Y. Tamminga

Thermal nitridation of silicon dioxide films

Thermal SiO2 films, ranging in thickness from 200 to 1200 A, were thermally nitrided using NH3 at temperatures between 800 and 1160 °C and for times varying between 3 min and 5 h. The resulting films were analyzed with Auger electron spectroscopy in combination with argon ion sputtering, Rutherford backscattering spectrometry, spectroscopic ellipsometry, and infrared spectroscopy. The nitridation results in the formation of oxynitride layers in the oxide, the largest nitrogen concentration being found in the surface region and at the SiO2/Si interface. The reaction proceeds via a replacement of oxygen by nitrogen atoms under the action of hydrogen. Although the amount of nitrogen incorporated in the surface region is independent of the original oxide thickness, the interface nitrogen concentration is lower the larger the oxide thickness. This can be explained by assuming that the diffusion of NHx (0<x≤3) through the oxide limits the reaction rate. In the temperature range 1000–1160 °C the rate of the reac...

Island growth in the atomic layer deposition of zirconium oxide and aluminum oxide on hydrogen-terminated silicon: Growth mode modeling and transmission electron microscopy

Atomic layer deposition (ALD) is used in applications where inorganic material layers with uniform thickness down to the nanometer range are required. For such thicknesses, the growth mode, defining how the material is arranged on the surface during the growth, is of critical importance. In this work, the growth mode of the zirconium tetrachloride∕water and the trimethyl aluminum∕water ALD process on hydrogen-terminated silicon was investigated by combining information on the total amount of material deposited with information on the surface fraction of the material. The total amount of material deposited was measured by Rutherford backscattering, x-ray fluorescence, and inductively coupled plasma–optical emission spectroscopy, and the surface fractions by low-energy ion scattering. Growth mode modeling was made assuming two-dimensional growth or random deposition (RD), with a “shower model” of RD recently developed for ALD. Experimental surface fractions of the ALD-grown zirconium oxide and aluminum oxid...

Deposition and composition of silicon oxynitride films

Silicon oxynitride (SiOxNy) films have been grown by a low‐pressure chemical vapor deposition (LPCVD) process from mixtures of SiH2Cl2, N2O, and NH3 at 820 °C. The overall layer composition can be varied by adjusting the N2O/NH3 gas flow ratio. Rutherford backscattering and Auger analysis of the films indicated a uniform composition throughout the layer, irrespective of the nature of the substrate. Both the thickness and the composition of these oxynitride films can conveniently be measured with ellipsometry; the oxygen to nitrogen ratio can be derived reliably from the value of the refractive index. It is inferred that LPCVD oxynitrides are homogeneous on an atomic scale, i.e., the silicon atoms are randomly surrounded by oxygen and nitrogen atoms, and are therefore not to be conceived of as a physical two phase mixture of silicon oxide and silicon nitride. Their stability in metal–oxynitride–oxide–silicon structures is found to improve with increasing oxygen content as regards flatband voltage shift upon temperature‐bias stress.

Aluminum‐silicide reactions. I. Diffusion, compound formation, and microstructure

Material reactions as a result of thermal treatment were studied on thin‐film Al/silicide/Si systems with CoSi2, PtxNi1−xSi, and MoSi2 for the silicide. Auger electron spectroscopy and Rutherford backscattering analysis showed the transport of Si and the metal released from the silicide into the Al and transport of Al into the silicide. X‐ray diffraction showed the formation of Co2Al9 at 400 °C, PtAl2, NiAl3, and PtNiAl2 at 275 °C, of which the latter disappeared above 450 °C, and MoAl12 at 535 °C, as well as free Si. The Co2Al9 formation followed a linear time dependence with an activation energy of 2.3 eV. The MoAl12 formation followed a parabolic time dependence with an activation energy of 3.6 eV. A thin tungsten layer between Al and the silicide proved to be effective as a diffusion barrier below 500 °C, at which temperature WAl12 was formed. The microstructure was studied by scanning and transmission electron microscopy, electron microprobe analysis, and scanning Auger electron spectroscopy. The rea...

Cellular structure and silicide formation in laser‐irradiated metal‐silicon systems

Laser irradiation of thin Co, Mo, and Pd films on single‐crystalline silicon using Q‐switched Nd‐YAG laser pulses was shown by He backscattering to result in deep metal penetration into the Si. Evidence of the silicide formation was obtained by x‐ray diffraction. Transmission electron microscopy showed the simultaneous occurrence of two types of cells with metal‐rich walls: small cells of about 0.1‐μm diameter, attributed to rapid solidification from a supercooled melt, and larger cells of about 1‐μm diameter, attributed to convection in the melt (Benard cells).

Characterization of low‐pressure chemical‐vapor‐deposited and thermally‐grown silicon nitride films

Low‐pressure chemical vapor‐deposited (LPCVD) silicon nitride films on silicon have been characterized by means of Rutherford backscattering (RBS), Auger electron spectroscopy (AES) combined with ion sputtering, and spectroscopic ellipsometry. It appeared that all LPCVD samples in the examined thickness range of 50 –500 A had an oxygen‐containing layer equivalent to 15–20 A of SiO2 at the nitride‐silicon interface. This interfacial layer originates from the native silicon oxide present at the silicon substrate when the deposition of nitride is started. For comparison, oxide‐free silicon substrates were nitrided in ammonia at temperatures between 800–1160 °C. The thermal nitride films were found to be very thin, at the most 30 A, even after 5 h of nitridation. Both the LPCVD and thermal nitride films oxidize slightly when transferred into the ambient; a surface layer equivalent to 8 A of SiO2 was detected. Auger and RBS results agree very well for all nitride films investigated. It is shown that RBS can be...

Plasma oxidation of thin aluminum layers for magnetic spin-tunnel junctions

This article presents results of a study initiated to characterize the plasma-oxidation process of very thin Al films, a technology commonly used to produce good barrier layers for magnetic spin-tunnel junctions. The behavior of oxygen in the oxidizing Al layer is determined using both quantitative (Rutherford backscattering spectrometry, transmission electron microscopy) and qualitative (x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry) analytical techniques. We have applied in situ XPS and experimented with 18O2 to unravel details of the oxidation mechanism. In addition, the influence of the oxygen pressure on the oxidation rate was established, both with and without a plasma being present. From optical emission spectra it is concluded that this pressure has a minor effect on the relative abundance of excited species in the oxygen plasma. When combined, these data constitute the basis of a model that distinguishes several steps in the plasma oxidation of Al. At the start, oxygen p...

Boron diffusion in amorphous silicon and the role of fluorine

We demonstrate that boron diffuses at high concentrations during low-temperature thermal annealing in amorphous silicon pre-amorphized by germanium ion implantation. For a typical boron ultrashallow junction doping profile, concentrations as high as 2×1020 cm−3 appear to be highly mobile at 500 and 600 °C in the amorphous silicon region before recrystallization. In crystalline silicon at the same temperatures the mobile boron concentration is at least two orders of magnitude lower. We also show that boron diffusivity in the amorphous region is similar with and without fluorine. The role of fluorine is not to enhance boron diffusivity, but to dramatically slow down the recrystallization rate, allowing the boron profile to be mobile up to the concentration of 2×1020 cm−3 for a longer time.

Groups III and V impurity solubilities in silicon due to laser, flash, and solid-phase-epitaxial-regrowth anneals

In this work the authors studied impurity solubilities of groups III and V elements in silicon resulting from laser anneal, flash anneal, and solid-phase-epitaxial regrowth. Rutherford backscattering channeling analysis was used to determine substitutional impurity depth profiles generated from the difference between the random and aligned spectra. Despite the large difference in peak temperatures and times, the anneals produce similar results with maximum solubilities beating the maximum equilibrium values by one to two orders of magnitude depending on the impurity. The correlation between the metastable solubility and the equilibrium distribution coefficient allows a prediction of values for other impurities not extracted experimentally.

Effectiveness of polycrystalline silicon diffusion sources

Boron and arsenic concentration profiles, diffused from polycrystalline silicon (polysilicon) into the underlying‐single crystalline silicon (mono) substrate, were analyzed by Rutherford backscattering spectrometry and secondary ion mass spectrometry for various levels of oxygen concentration at the poly/mono interface. In contrast with previous reports it was found that chemically grown interfacial oxide layers of about 1.4‐nm thickness provide more effective diffusion sources than oxygen‐free interfaces. This surprising phenomenon is caused by the strong correlation between the crystalline structure of the polysilicon layer and the diffusion rates of dopant species in that layer. It is shown that the small amount of oxide at the poly/mono interface prevents the epitaxial realignment of the polysilicon, thereby maintaining high diffusion rates in the polysilicon, without offering a significant barrier to the diffusion of boron and arsenic across the interface.