Sputtering Behavior Research Articles

Sputtering effect of gas cluster ion beams

Sputtering effects of CO 2 cluster ion beams have been studied in comparison with the effect of monomer ions. A surface smoothing effect was obtained for Au, Pt, Cu, poly-Si, SiO 2 and Si 3N 4 films, Si substrates and Soda-lime glasses. The energy dependence of smoothing and sputtered depth was different, and a higher ratio between reduction of surface roughness and sputtered depth was obtained at lower cluster energy. Surface smoothing can be achieved by cluster ion irradiation even at 5 keV. Cluster ion irradiation-induced sputtering produced very flat surfaces due to a different sputtering behaviour from monomer ions, which is expressed as lateral sputtering.

Practical aspects for the use of plasma emission monitoring in reactive magnetron sputtering processes

The sensitivity of Plasma Emission Monitoring (PEM) depends on both target material and oxygen mass flow at least for indium and tin target. Optical emission intensity and cathode voltage were recorded for several argon and oxygen flows in various tin and indium oxide thin film fabrication experiments, with the magnetron working in constant current mode. The results obtained indicate marked differences between indium and tin targets, as far as their reactive sputtering behaviour is concerned. A theoretical explanation is proposed for the observed target voltage variations with increasing oxygen mass flow in relation to the corresponding optical emission intensities.

Radio frequency sputtering and the deposition of high-temperature superconductors

This paper reviews the background to glow-discharge sputter deposition of thin films and the deposition of YBCO superconducting thin films in particular. The background to sputtering is briefly reviewed with reference to the recent literature on analytical and numerical techniques for investigating radiofrequency (r.f.) plasmas, magnetron sputtering and hysteretic behaviour in reactive sputtering. Low-energy, ion-assisted deposition techniques are briefly reviewed, and the effect of ion-beam interactions on film nucleation and growth is also discussed. The background to the sputter deposition of high-temperature superconductors (HTS) is given along with the choice of sputtering system for HTS deposition. Resputtering effects, off-axis andin-situ/ex-situ processing are also discussed. The sputter deposition of YBa2Cu3O x is considered in detail along with theP-T-x oxidation conditions and the tetragonal/orthorhombic line. Typical experimental arrangements and results for YBCO sputtered onto SrTiO3 and MgO are given. The problem of producing high-critical-current-density polycrystalline films by sputtering is also discussed.

Surface binding energies of alloys: a many-body approach

The surface binding energy of atoms is a crucial quantity for determining the sputtering behaviour of a sample under energetic atom bombardment. We study the surface binding energy of a binary alloy using a many-body interaction potential of the tight-binding type; analytical calculations are checked against molecular-statics computer simulations. As a result, we find a linear dependence of the surface binding energy of each species on its concentration. Quantitatively, its behaviour can be derived from the properties of the pure substances. The influence of the chemical energies of mixing is only small. These results correspond qualitatively to those of a pair-potential model, which are well known. The differences are of a quantitative nature. While these results have been derived for an undamaged surface, we also discuss the sputtering behaviour under steady-state conditions.

Sputtering behaviour of stainless steel during Pt ion implantation

The sputtering behaviour of stainless steel during 1500 keV Pt ion bombardment was investigated. Progressively higher doses of Pt were implanted into stainless steel and the retained dose determined in order to produce a saturation curve. The experimentally determined sputter yield suggested by this curve is significantly lower than that predicted by the commonly used method of Matsunami et al. The results also suggest preferential sputtering of Pt following erosion into the implanted region.

Examinations regarding the correctness of quantitative surface analysis using SNMS

For the assessment of the correctness of depth profile analyses with non-ideal technical metal surfaces using secondary neutral particle mass spectrometry (SNMS), the roughness of the sample surface was examined for the transition width of the signal. It is shown that with elements with low sputter rates (Al Mn), similar to that of the substrate element (Fe), there is no significant influence of the roughness. However, clear dependencies are observed for tin and zinc, elements with high sputter rates. Whereas tin gave acceptable results when the roughness was significant, cone formation was observed with zinc which caused abnormal sputter behaviour. The use of high-frequency sputter processes eliminates this cone formation and leads to constant signals, even with thick zinc layers. This method is therefore not only suitable for use with non-conductors, as originally planned, but also offers considerable advantages in the analysis of metal coatings.

Sputtering behavior of boron and boron carbide

Sputtering yields of boron were measured with D + and B + ions for normal and oblique angles of incidence. Self-sputtering data of boron carbide were simulated in the experiment by using Ne + ions. The energies of the impinging ions were between 20 eV and 10 keV. The measured data are compared with computer simulated values calculated with the TRIM.SP program. The boron data for normal ion impact are higher than the calculated values, whereas those for oblique ion incidence are smaller than the calculation predicts. This discrepancy is explained by the surface roughness and supported by SEM micrographs. The comparison of the boron carbide data with TRIM.SP calculations shows much better agreement than the boron data. In this case the target surface was much smoother.

Influence of manufacturing process of indium tin oxide sputtering targets on sputtering behavior

Thin films of In 2O 3+SnO 2 (indium tin oxide or ITO) have wide utility because they are electrically conductive and transparent at visible wavelengths. A preferred method for making highest quality ITO coatings is reactive sputtering from targets of mixed indium and tin oxides. The resulting film properties are highly dependent upon the deposition conditions, and upon post-deposition film treatments. Film data and sputtering efficiency are also effected by sputtering target characteristics. This study evaluated the influence of the targets on the electrical resistivity of deposited ITO films, and the effect of target properties on the sputtering rate. A matrix of 12 targets was tested; all had composition 90 wt.% In 2 O 3+10 wt.% SnO 2. The effects of varying target density, degree of target oxide reduction from complete stoichiometry, and target purity were measured. The results are, in summary, (1) partial reduction of oxide targets from complete stoichiometry does not influence film resistivity, (2) the data indicate a small (perhaps negligible) dependence of film resistivity upon target density, (3) higher target density tends to promote enhanced deposition rate, and (4) purposeful addition of silicon, aluminum, magnesium, calcium, and sodium at high levels to ITO targets degrades film resistivity depending upon the total concentration of impurities added, but independently of the contaminating species.

Ion sputter effects on HgTe, CdTe, and HgCdTe

Preferential ion sputtering of HgTe and HgCdTe is the dominant ion sputter effect observed in these material systems. There is little preferential sputtering of CdTe. The ion sputter behavior of HgCdTe can be predicted from the ion sputter behavior of HgTe and CdTe. The weakness of the Hg–Te bond compared to the Cd–Te bond accounts for the greater ion sputter rate of HgTe to CdTe and causes Hg to have a large relative ion sputter yield compared to the other elements and, most likely, plays a dominant role in the preferential sputtering of Te in HgCdTe. Preferential ion sputtering is dependent on the chemistry of Hg1−xCdxTe; elemental ion sputter yields depend on the amount of HgTe in the sample.

Temperature-dependent sputtering of doped graphites and boron carbide

Abstract The temperature dependence of the sputtering behaviour of various low-Z materials is presented. The hydrocarbon production under deuterium bombardment is investigated as a function of the target temperature. Carbon doped with beryllium or boron, as well as boron carbide show a strong reduction in the chemical sputtering yield. The reduction of the radiation-enhanced sublimation yield (RES) above 1200 K is small and not uniquely correlated with the dopant concentration. A variety of doped graphites is compared for 1 keV D+ sputtering at 300, 800 and 1470 K. The resulting erosion yields are discussed in terms of dopant concentration and the microstructure of the materials.

Molecular-dynamics simulations of bulk and surface damage production in low-energy Cu→Cu bombardment

Molecular-dynamics simulations are employed to study in detail the effects of low-energy (≤100 eV) bombardment of a Cu (001) surface by Cu atoms. By following the simulation up to 4 ps in real time, the end configuration of defects in the target can be observed. We present results on the vacancy and interstitial distribution in the target, the spontaneous defect recombination, the number of surface vacancies and adatoms produced, and the mixing of target atoms induced by the bombardment. Furthermore, the fate of the projectile atom−backscattering and implantation−and the sputtering behavior are investigated. The relevance of the results on the modelling of ion-beam (assisted) deposition is discussed.

Highly selective sputtering of silicon from TiSi2 at elevated temperature

We demonstrate almost 100% selective sputtering of silicon from TiSi2 using a combination of low energy ion bombardment and elevated temperature. TiSi2 was prepared by annealing 1000-Å-thick Ti on (100)Si in He at 635 °C for 30 min to produce 2300-Å thick TiSi2. Ion beam etching was carried out using 300 eV argon with a flux of 0.27 mA/cm2 at temperatures from 33 to 700 °C. In situ sheet resistance measurements were used to monitor the decrease in silicide thickness as a function of time. Near room temperature, ion etching causes normal sputtering of the silicide. However, at temperatures of 500–700 °C, the sheet resistance remains almost unchanged during ion beam etching. Analysis by Rutherford backscattering, with and without Xe markers, shows that Si atoms sputtered from the surface of these high-temperature samples are continuously replaced by Si diffusing from beneath the silicide layer. The thickness and composition of the silicide remain almost unchanged, but the dramatic change in sputtering behavior shows that the surface is enriched in Si. Compared with the room-temperature values, the absolute sputtering yield of Ti at 500–700 °C is decreased by a factor of 5, and the yield of Si is increased by a factor of 2. The net result is almost 100% selective sputtering of silicon.

AES study of amorphous Fe 100− xB x ( x = 14–25 at.%) alloys

Auger electron spectroscopy in conjunction with argon ion sputtering was used to study the sputtering behaviour of melt-spun amorphous Fe 100− x B x ( x = 14–25 at.%) alloys. Measurement of equilibrium surface composition using the low energy peak of iron Fe(47 eV, MVV) indicated an enrichment of boron in the sputter altered layer in all alloys for argon ion energies of 1 keV and 3 keV. The corresponding sputtering yield ration ( Y Fe Y B ) had a value between 1.3 and 1.6. The surface composition, calculated by using the high energy iron peak (651 eV, LMM), indicated depletion of boron in the sub-surface region in comparison to that measured by using the low energy peak. It appears that binding effects rather than mass play a significant role in determining the preferential sputtering behaviour of these alloys and the possible sputtering mechanisms could involve cascade sputtering and/or surface segregation. The plot of surface composition or the sputter yield ration versus boron atom fraction in the bulk showed a break at 18 at.% boron. This is attributed to the known structural differences in FeB amorphous alloys. Analysis of native oxide films on these alloys showed enrichment of boron near the oxide-alloy interface and the film thicknesses were approximately in the range 4–6 nm. It was inferred from an analysis of the low energy Auger peaks that the oxide films consisted of Fe 3+, Fe 2+ and B 3+ species.

Depth profiling of catalyst samples: An XPS-based model for the sputtering behavior of powder materials

A model is presented to describe the depth profiles obtained by ion-bombarding polycrystalline multicomponent samples. Different calculations for idealized catalyst structures illustrate the possibilities of using the ion-sputtering technique for the characterization of catalysts. These calculations show that the depth profiles obtained using dispersed phase XPS intensities may provide semi-quantitative information on particle size, existence of solid solution, or formation of mono- or bimetallic particles in bimetallic catalysts. Examples with the dispersed phase in metallic or oxide forms that illustrate these applications are presented.

Modeling of multicomponent reactive sputtering

Computer process modeling has become an important tool in the development of new thin-film processes. Previously, we presented a model that successfully describes the complex behavior of the reactive sputtering of a single-element target. The model enables one to predict, e.g., the hysteresis effect and the composition of the deposited film. There exists, however, a demand for developing reliable reactive-sputtering processes for more complicated materials. This calls for an extended reactive-sputtering model including more than one target element. In this article, we will for the first time present an extension of our previous model now taking the effect of multicomponent targets into consideration. The transition from metallic- to compound-sputtering mode normally occurs at different levels for different single-element targets. The new extended reactive-sputtering model predicts the transition from metallic to compound mode during multicomponent reactive sputtering of thin films. The results indicate that under normal operating conditions, only one transition region exists irrespective of the number of target elements involved in the process. This is experimentally verified for the process of reactive cosputtering of Al+Ti in an Ar/O2 atmosphere. We will also point out the complex composition behavior of the reactive-cosputtering process as compared with reactive sputtering from an alloy target.

The effects of elevated temperature on sputter depth profiles of silver/nickel bilayers

The effect of elevated temperature on the sputtering behavior of silver/nickel bilayers was studied using Auger electron spectroscopy and argon ion sputtering while specimens were held at elevated temperatures (25, 135, 235, 335, and 435 °C). We find that the silver overlayer tranforms from a layer to islands during ion sputtering at temperatures above 100 °C. The transformation to islands is thought to relieve film stresses caused by film-growth and/or lattice mismatch. Surface diffusion of silver is also observed at elevated temperature (>100 °C). This causes the lower surface energy metal (Ag) to cover the higher surface energy metal (Ni) in regions between the islands. These experiments show that properties of the system such as the heat of mixing, and the surface and interface energies need to be considered when the sputter depth profiling technique is used to study thin film structures, particularly when sputtering is performed at elevated temperatures.

Secondary Ion Mass Spectrometry Studies of Polycrystalline Thin-Film Cdte/Cds Solar Cells

Polycrystalline thin films of CdTe deposited on CdS are one of the most promising materials systems currently being investigated for the fabrication of low cost, large area, high efficiency photovoltaic devices. However, many of the deposition processes being used to fabricate these thin film materials have not yet been well characterized. It has been found that a post-fabrication heat-treatment is necessary to improve the quantum efficiency of these devices. Secondary ion mass spectrometry (SIMS) was used to study the interdiffusion of S and Te in CdTe/CdS structures grown by two different methods. The depth profiles revealed significant differences in the sputtering behavior depending on the film morphology.Two sets of CdTe/CdS samples were studied. The first set of films was deposited at high temperature using a spray pyrolysis technique with no post deposition anneal. The second set of films was electroplated, followed by treatment with CdCl2 and a high temperature anneal.

Hysteresis behaviour of silver sputtered in different plasma atmospheres at constant flow rates

The effects of ion bombardment on sputtering behaviour of pure silver targets in inert and active gas atmospheres were investigated, using a dc planar magnetron sputtering system. The obtained current-voltage characteristics showed the formation of hysteresis loops without noticeable sharp transitions. Redeposited layers of silver nitride or silver oxide on the target surface when using nitrogen or oxygen in the glow discharge, residual ionization when using dry argon atmosphere were considered the main reasons for the occurence of these loops. The results indicate that films of AgNx and AgOx can be deposited with controlled x in the range 0 ⩽ x ⩽ 1 using voltage control at constant gas flow rates.

Etching mechanisms of polymers in oxygen microwave multipolar plasmas

A parametric study of polymer etching in an oxygen microwave multipolar plasma with independent rf wafer biasing is reported. The etch rate evolution as a function of atomic oxygen concentration, measured by actinometry, indicates a monolayer adsorption kinetics for the photoresist/oxygen system. Furthermore, a step-like variation in the etch rate with ion bombardment energy is observed. In the low-energy range, where sputtering effects are negligible, ion-induced chemical etching is the main etching component. In the high-energy range, an additional etching which exhibits sputtering behavior arises.

The primary ion energy dependence of the analyzing depth in SIMS measurements

The analyzing depth in a SIMS measurement (2–12 keV) has been studied on a nickel deposited (50 Å) copper substrate by observing sputtering behavior of the specimen with the method reported by the authors [Surface Sci. 177 (1986) 229]. The relation between the obtained analyzing depth and the ion energy show on a logarithmic scale a good linear relationship. Taking account of these results, the analyzing depth of the SIMS measurement is closely related to the projected range of the incident ion. For the ions in the energy range of 2–3 keV, the analyzing depth is almost the same as the projected range. The obtained analyzing depth is 28 Å at 2 keV and 56 Å at 12 keV.