Showing papers in "Journal of Vacuum Science & Technology B in 1992"

GaN, AlN, and InN: A review

Abstract: The status of research on both wurtzite and zinc‐blende GaN, AlN, and InN and their alloys is reviewed including exciting recent results. Attention is paid to the crystal growth techniques, structural, optical, and electrical properties of GaN, AlN, InN, and their alloys. The various theoretical results for each material are summarized. We also describe the performance of several device structures which have been demonstrated in these materials. Near‐term goals and critical areas in need of further research in the III–V nitride material system are identified.

Relaxed GexSi1−x structures for III–V integration with Si and high mobility two‐dimensional electron gases in Si

Abstract: To obtain a large lattice constant on Si, we have grown compositionally graded GexSi1−x on Si. These buffer layers have been characterized with electron‐beam‐induced current, transmission electron microscopy, scanning electron microscopy, x‐ray diffraction, and photoluminescence to determine the extent of relaxation, the threading dislocation density, the surface morphology, and the optical properties. We have observed that it is possible to obtain completely relaxed GexSi1−x layers with 0.1

Microscopic uniformity in plasma etching

Abstract: As we enter the era of ultra‐large‐scale integrated circuit manufacture, plasma etching grows more important for fabricating structures with unprecedented dimensions. For feature sizes below 1 μm and aspect ratios (depth/width) much larger than one, etching rates have been observed to depend on aspect ratio and pattern density. Such dependencies tend to increase the cost of manufacturing because even small changes in device design rules, cell design, or wafer layout can result in time‐consuming, new plasma process development. In addition, microscopically nonuniform etching affects the trade‐off between chips lost from failure to clear and chips lost by damage from overetching. Although aspect ratio and pattern dependent etching have been observed for a large variety of material systems and processing conditions, the fundamental causes underlying these effects are poorly understood. Partly, this results from use of confusing and conflicting nomenclature and a lack of careful, quantitative comparisons between experiment and theory. In this article we review recent literature on microscopic uniformity in plasma etching and carefully define terminology to distinguish between aspect ratio dependent etching (ARDE) and the pattern dependent effect known as microloading. For ARDE, we use dimensional analysis to narrow the range of proposed mechanisms to four which involve ion transport, neutral transport, and surface charging. For microloading, we show that it is formally equivalent to the usual loading effect, where the reactant concentration is depeleted as a result of an excessive substrate load.

Dependence of the quality factor of micromachined silicon beam resonators on pressure and geometry

Abstract: An experimental study of damping and frequency of vibrating small cantilever beams in their lowest eigenstate is presented. The cantilever beams are fabricated from monocrystalline silicon by means of micromachining methods. Their size is a few millimeters in length, a few 100 µm in width, and a few 10 µm in thickness. Damping and resonance frequency are studied as a function of the ambient pressure p (1–105 Pa) and the geometry of the beam. The purpose of this research was to obtain design rules for sensors employing vibrating beams. The analysis of the experimental results in terms of a semiqualitative model reveals that one can distinguish three mechanisms for the pressure dependence of the damping: viscous, molecular, and intrinsic. For viscous damping a turbulent boundary layer dominates the damping at high pressures (105 Pa), while at smaller pressure laminar flow dominates. In the latter region, this leads to a plateau for the quality factor Q and in the former to Q p. The pressure pc at which the transition from laminar flow dominated damping to turbulent flow dominated damping occurs depends on the geometry of the beams. pc is independent on the length and decreases with both, the width and the thickness of the beams.

Recent developments in ohmic contacts for III-V compound semiconductors

Abstract: Recent advances in the technology and understanding of ohmic contacts for a variety of III–V compound semiconductor material systems are reviewed. Special attention is focused on factors and critical issues involved in making low resistance and reliable ohmic contacts. The solid‐phase regrowth mechanisms of key metallization systems are described. In addition, special techniques to improve the ohmic contacts are discussed. Finally, the reliability issues of ohmic contacts are addressed.

Effect of dislocations on the electrical and optical properties of long‐wavelength infrared HgCdTe photovoltaic detectors

Abstract: The quantitative effects of dislocations on the electrical and optical properties of long‐wavelength infrared (LWIR) HgCdTe photovoltaic detectors was determined by deliberately introducing dislocations into localized regions of two high‐performance arrays having cutoff wavelengths of 9.5 and 10.3 μm at T=78 K. Results show that dislocations can have a dramatic effect on detector R0A product, particularly at temperatures below 78 K. For large dislocation densities, R0A decreases as the square of the dislocation density; the onset of the square dependence occurs at progressively lower dislocation densities as the temperature decreases. A phenomenological model was developed which describes the dependence of the detector R0A product with dislocation density, based on the conductances of individual and interacting dislocations which shunt the p–n junction. Spectral response and quantum efficiency are only weakly affected, as is the diffusion component of the leakage current. The 1/f noise current was found t...

Properties of CdZnTe crystals grown by a high pressure Bridgman method

Abstract: CdZnTe crystals have been grown over the full range of alloy composition by a high‐pressure Bridgman (HPB) method. Use of the inert gas over pressure reduces loss of material from the melt, and permits growth without the use of sealed ampoules, extending the range of possible alloys, and allowing a choice of crucible materials. The HPB method yields high‐quality CdZnTe and enables room‐temperature gamma radiation detectors to be made over large area wafers of undoped material for the first time.

Simulation of profile evolution in silicon reactive ion etching with re‐emission and surface diffusion

Abstract: This article describes a model that simulates etching profiles in reactive ion etching. In particular, models are developed to explain the significant lateral etch rate that is observed in many etch profiles. The total etch rate is considered to consist of two superimposed components: an ion‐assisted rate and a purely ‘‘chemical’’ etch rate, the latter rate being due to etching by radicals in the absence of ion bombardment. The transport of radicals to the evolving interface is studied for two different transport mechanisms: re‐emission from the surface and diffusion along the surface. For the case of transport by surface re‐emission, a reactive sticking coefficient is defined for the radicals, and a formulation is developed to simulate etching for any value (between zero and unity) that this sticking coefficient may assume. When the sticking coefficient approaches either zero or unity, the method of characteristics is shown to be useful for profile simulation. Transport of radicals by surface diffusion is also investigated, and it is shown that the important dimensionless parameter governing profile evolution is the Damkohler number. The two models are compared to experiments performed on the etching of silicon in a SF6 plasma, and the surface re‐emission model is shown to accurately predict the development of etching profiles.

1/8 μm optical lithography

Abstract: The critical bottleneck to extending optical lithography down to the 1/8 μm level is the performance of the projection optics. The Markle–Dyson configuration is virtually free of all geometric and chromatic aberrations. A prototype system has been constructed and characterized. The system uses 248 nm light from a mercury arc lamp at a numerical aperture of 0.7. 0.25 μm resolution has been demonstrated with non phase shifting masks: using phase shifting Levenson‐type masks, a grating consisting of 0.125 μm lines and spaces has been printed. Two possible extensions of the existing design are proposed which would allow general 1/8 μm geometries to be patterned. The first is a 0.7 numerical aperture (NA) system working at a wavelength of 157 nm, and the second is a 1.05 NA immersion system working at 193 nm. At these high NAs the depth‐of‐focus (DOF) of the image becomes very small if a clear aperture is used. However, if the aperture is apodized, the DOF can be increased considerably, and a procedure for opt...

Arrayed miniature electron beam columns for high throughput sub-100 nm lithography

Abstract: In recent years, considerable progress has been made on an approach based on a novel concept which combines scanning tunneling microscope, microfabricated lenses, and field emission technologies to achieve microminiaturized low‐voltage electron beam columns with performance surpassing the conventional column. High throughput lithography is a potentially very important application for these microfabricated columns which measure only millimeters in dimensions. This is to be achieved using an array of these minicolumns in parallel in a multibeam mode with one or more columns per chip. The low‐voltage operation is attractive because proximity effect corrections may not need to be applied. In addition, an arrayed microcolumn system also has the potential of reducing the cost of the overall system through the compaction of the mechanical system. The throughout advantages for such an arrayed system based on different beam forming optics and pattern generation approaches will be discussed. In addition to lithography, a wide range of other applications for such an arrayed system such as testing, metrology, storage, etc., can also be considered.

Schottky barrier height and negative electron affinity of titanium on (111) diamond

Abstract: Titanium was deposited on a natural type IIb diamond surface with a (111) orientation. The titanium‐diamond interface was studied with ultraviolet photoemission spectroscopy, using 21.2 eV light. Prior to deposition, the diamond was chemically cleaned, and a sharp (0.5 eV full width at half‐maximum) peak was observed at the position of the conduction band, indicating a negative electron affinity surface. After a subsequent argon plasma clean this peak disappeared, while the spectrum shifted 0.5 eV towards higher energies. Upon submonolayer titanium deposition the spectrum shifted 0.5 eV down, while the negative electron affinity peak reappeared. Further titanium depositions caused this titanium induced negative electron affinity peak to be attenuated, indicating that the emission originated from the interface. By determining the relative positions of the diamond valence band edge and the titanium Fermi level, the Schottky barrier height of titanium on diamond (111) was measured and found to be 1.0±0.2 eV....

Properties of silicon dioxide films deposited at low temperatures by microwave plasma enhanced decomposition of tetraethylorthosilicate

Abstract: Silicon dioxide films have been deposited at low temperatures (200–250 °C) by microwave plasma enhanced decomposition of tetraethylorthosilicate (TEOS). The effects of the presence of oxygen in the discharge in film deposition rate, mechanism, and the physical properties of the films have been investigated. Structural characterization of the deposited films has been carried out by etch rate measurements, infrared transmission spectra, x‐ray photoelectron spectroscopy, Auger, and secondary ion mass spectrometry analyses. Films deposited using TEOS and oxygen have confirmed a density comparable to standard silane‐based low‐pressure chemical vapor deposition and plasma enhanced chemical vapor deposition oxides, nearly perfect stoichiometry, extremely low sodium and carbon content, and the absence of many undesirable hydrogen related bonds. Various electrical properties, viz., resistivity, breakdown strength, fixed oxide charge density, interface state density, and trapping behavior have been evaluated by the...

Key issues in HgCdTe‐based focal plane arrays: An industry perspective

Abstract: Technological limits, not fundamental issues, are all that keep HgCdTe from completely dominating almost all infrared (IR) applications. The technological limits result from our incomplete understanding of HgCdTe materials science. This article’s snapshot view, from the unique perspective of the major United States HgCdTe IR detector array companies, suggests directions that HgCdTe detector technology should take as we approach the next century. We argue that the Government, industrial users, and industrial producers of HgCdTe must support continuing scientific investigation of this material to parallel the manufacturing of second generation HgCdTe‐based systems. Without this manufacturing science base, systems will develop too slowly, cost too much, and fail too often. To assist developing this critically important technology, the article highlights some of the more vexing and as yet unsolved HgCdTe materials science and engineering problems that we see as being important.

Oxidation of sub-50 nm Si columns for light emission study

Abstract: Understanding the optical and electrical properties of Si nanostructures is essential for exploring the potential of using structural quantum confinement to induce light emission from crystalline Si. To this end, sub‐50 nm Si columns were fabricated with high resolution electron beam lithography and anisotropic reactive ion etching. The dimensions of the Si nanostructures were further reduced by thermal oxidation. A novel transmission electron microscopy technique was developed to monitor the oxidation progress without removing the oxide structural support. Images of sub‐5 nm crystalline Si cores were obtained. The oxidation rates of the Si nanostructures were characterized. Among the various interesting oxidation phenomena are the nonmonotonic oxidation rate with respect to the column size and an unexpectedly slow change of the outer diameters of the oxidized columns. Several likely mechanisms, including the stress retardation of oxidation for a small radius of curvature, the stress induced generation an...

Recipe to minimize Te precipitation in CdTe and (Cd,Zn)Te crystals

Abstract: Using a quasichemical approach, the total native defect concentration and the minimum deviation in stoichiometry have been calculated in CdTe crystals as a function of the Cd pressure at various temperatures. With this knowledge, CdTe and (Cd,Zn)Te wafers have been subjected to postgrowth step annealing treatment under conditions such that the crystals are in equilibrium with a Cd or (Cd,Zn) vapor corresponding to the minimum in deviation from stoichiometry at each annealing temperature. The step annealed CdTe and (Cd,Zn)Te wafers have been examined under infrared microscopy and have shown significant reduction in the concentration of Te precipitates, whereas the unannealed wafers have had numerous Te precipitates distributed throughout the bulk. HgCdTe epitaxial films have been grown on the step annealed CdTe and (Cd,Zn)Te wafers as well as on unannealed wafers from the same boule. Examination of the cross sections of the epitaxial films indicates appearance of Te precipitates in films grown on unanneale...

Laser‐chemical three‐dimensional writing for microelectromechanics and application to standard‐cell microfluidics

Abstract: A high‐speed technique has been developed for machining three‐dimensional silicon parts using laser‐induced chlorine etching reactions. Parts are created directly from solid‐modeling computer‐aided‐design/computer‐aided‐manufacturing software. Removal rates exceeding 2×104 and ≥105 μm3/s are achieved at 1 and 15 μm x–y resolution, respectively. This is several orders of magnitude faster than electrodischarge machining methods. Submicrometer resolution has been achieved. Laser‐induced metallization of resulting structures as well as replication through compression molding have been demonstrated. A class of microfluidic flow‐channel devices is under development using a standard‐cell software architecture combined with field stitching.

Focused ion beam deposition of Pt containing films

Abstract: Focused ion beam induced deposition of platinum films from a gas of methylcyclopentadienyl trimethyl platinum is reported. Deposition was carried out with a 25 kV beam of Ga+ with current densities of 2–7 A/cm2 that was controlled by a digital scan generator. Film yields and resistivity were measured as a function of beam current density, gas flux, scan dwell, and loop time. Relatively high yields of 1.4 μm3/nC and resistivities as low as 400 μΩ cm were measured for deposition carried out in 1×10−6 Torr background pressure of residual gas. Auger studies revealed that the films were surprisingly free of oxygen, but contained significant amounts of carbon. A figure‐of‐merit, Fm=ρ/Y, is defined which enables comparison of films used for interconnects. Fm for the Pt films is superior to that of W(CO)6 deposited W films.

Tunneling and 1/f noise currents in HgCdTe photodiodes

Abstract: The 1/f noise currents and the dc dark current–voltage characteristics are measured over a wide range of reverse bias voltages (0≤Vd≤−1.5 V) and operating temperatures (30–120 K). The diodes are fabricated by ion implanting boron (n+) on bulk p‐type material with x≊0.22. Native anodic sulfide in combination with deposited ZnS is used for surface passivation. The dc dark currents of the photodiodes are modeled to extract the tunneling currents from the measured dark currents. The modeling takes into consideration diffusion, generation–recombination, and the two types of tunneling currents (trap assisted tunneling and band to band tunneling). The measurements demonstrate that the dominant mechanism that produces 1/f noise in HgCdTe photodiodes is tunneling, in particular trap assisted tunneling. The correlation between the 1/f noise currents and the dc tunneling currents is given by In=α(It)β(f )−1/2, where It is the tunneling current. The empirical factors β and α are approximately β≊0.5 and α≊1×10−6 for a...

Characterization of near‐field holography grating masks for optoelectronics fabricated by electron beam lithography

Abstract: Direct write e‐beam lithography and reactive ion etching was used to fabricate square‐wave gratings in quartz substrates which serve as pure phase masks in the near‐field holographic printing of gratings. This method of fabricating these masks extends the flexibility of the printing technique by allowing both abrupt phase shifts as well as multiple grating pitches to be simultaneously printed from a single contact mask. Grating masks with periods in the 235–250 nm range have been produced and measured to be within 0.15 nm of the design period. Transmitted and diffracted beam powers have also been measured for various duty cycles and etch depths and are shown to be important parameters for ‘‘balancing’’ these interfering beams. Simple scalar diffraction modeling is used to qualitatively examine the dependence of diffraction on grating parameters, but the need for a more comprehensive modeling is illustrated. Prototype masks have been used to produce grating patterns on InP substrates using two different ul...

Work function, electron affinity, and band bending at decapped GaAs(100) surfaces

Abstract: Work function and band bending measurements are performed on n‐ and p‐type GaAs(100) surfaces prepared by molecular‐beam epitaxy and As decapping. The band bending is almost independent of the decapping temperature and surface reconstruction [(1×1)→C(4×4)→C(2×8)→(4×2)]. The work function and electron affinity undergo large and systematic variations of up to 400 meV which consistently establish maxima and minima of these quantities for the (2×4)‐C(2×8) and (4×2)‐C(8×2) structures, respectively. These variations are due to surface dipoles induced by charge exchanges between the cation and anion dangling bonds in the top two layers of the crystals. These charge exchanges are fully explained by applying a simple electron counting model to each reconstruction.

Evidence for an Eley–Rideal mechanism in the addition of hydrogen atoms to unsaturated hydrocarbons on Cu(111)

Abstract: The addition of hydrogen atoms to ethylene and benzene on a Cu(111) surface has been studied by temperature‐programmed desorption and integrated desorption mass spectrometry. The results show that adsorbed ethylene and benzene react with atomic hydrogen from the gas phase at temperatures as low as 110 K. The reaction intermediates, ethyl groups and partially hydrogenated benzene, can be isolated on the surface at this low temperature. When the surface is heated to above 150 K, hydrogen elimination reactions occur to produce ethylene, benzene, cyclohexadiene, and cyclohexene. Complete hydrogenation to alkanes also occurs for larger H‐atom exposures. The absence of these addition reactions when H atoms are adsorbed onto the surface before ethylene or benzene suggests Eley–Rideal mechanisms for these processes.

Low temperature thermal oxidation sharpening of microcast tips

Abstract: The authors report the fabrication of sharp tips by casting a tip material into a sharpened silicon mold whose original shape was modified by the growth of a nonuniform, low temperature, thermal oxide. The addition of the oxide layer is the only significant difference between this process and processes currently being used by the majority of commercial producers of atomic force microscope force sensing cantilevers. While commercially available molded tips typically have radii of curvature of approximately 500 A and aspect ratios of 0.5 or less, tips made in the modified molds have radii of curvature as low as 110 A and aspect ratios of 0.95. This technique is useful when sharpness, uniformity, and low cost are required.

The role of oxygen excitation and loss in plasma‐enhanced deposition of silicon dioxide from tetraethylorthosilicate

Abstract: The deposition rate of silicon dioxide from tetraethylorthosilicate/O2 capacitively coupled plasmas increases with increasing applied rf power, increasing total pressure and decreasing wafer temperature. These measured deposition rate dependences can be explained by a simple plasma deposition model in which deposition occurs through both an ion‐assisted and an oxygen atom initiated pathway. The relative contributions of these pathways were roughly isolated using limiting step coverage measurements on low aspect ratio trenches. Limiting step coverages decreased, and hence directionality increased, with increasing rf power density, decreasing total pressure, and increasing wafer temperature. A simple bulk plasma chemistry model combined with an analytical sheath model was developed to qualitatively explain our experimental findings. The model suggests that the ion‐enhanced deposition rate is directly proportional to oxygen ion flux, with a reactive sticking coefficient approaching unity. Using literature va...

Bias‐switchable dual‐band HgCdTe infrared photodetector

Abstract: The feasibility of an all molecular‐beam epitaxially (MBE) grown, bias‐switchable, dual‐band HgCdTe detector is demonstrated. Detection in the midwavelength infrared (MWIR) band only or the long‐wavelength band (LWIR) only is accomplished by the proper selection of detector bias in the ≥±100 mV range. The devices were all grown in situ by the MBE on CdZnTe or GaAs substrates and consisted of three intentionally doped layers in an n–p–n sequence. At 77 K the floating base two terminal devices responded to the ∼4.9–8 μm spectral band with the application of ≥−100 mV to the bottom contact and to the ∼2.1–4.9 μm band with the application of ≥0 mV. Quantum efficiency depended on bias with a maximum of 59% for LWIR and 66% for MWIR wavelengths at −150 mV and ≥0 mV, respectively. The operation of the dual‐band detector is discussed. Significant design differences between the heterojunction phototransistor and the dual‐band detector are noted.

Atom‐resolved imaging and spectroscopy on the GaAs(001) surface using tunneling microscopy

Abstract: Scanning tunneling microscopy and scanning tunneling spectroscopy have been used to investigate the structure and current–voltage [I(V)] characteristics of the molecular‐beam epitaxially grown, As‐rich GaAs(001)‐(2×4) surface. High‐resolution images reveal a modulation in the topography of the individual arsenic dimers measured with the tunneling microscope in the constant current mode. The observed features are attributed to an increased tunneling probability out of the occupied electronic lone pair states of the As dimers. The I(V) spectroscopy performed on the (001) surface of low doped n‐type GaAs samples differs considerably from the results obtained on the (110) surface of this semiconductor. This is attributed to band bending that is due to a lower doping concentration below the surface. The electrostatics involved in imaging with a tunneling microscope are described in a simple model, based on the depletion approximation, that accounts for the experimental results.

Electron‐beam induced tungsten deposition: Growth rate enhancement and applications in microelectronics

Abstract: Electron‐beam induced deposition (EBID) of tungsten from the precursor gas W(CO)6 was investigated with the aim of enhancing the growth rate of the process. By varying dwell and loop time over a limited range, experimental deposition rates were compared to a time dependent model developed to describe the focused ion beam induced deposition. We found the cross section σ for EBID at 30 keV beam energy to be 1.2±0.2×10−16 cm−2. Based on these data, we predicted the achievable growth rate as a function of the current density. Moreover, EBID was used for x‐ray and open stencil mask repair, the generation of etch masks and the deposition of electrically conductive lines. The resistivity of the latter was found to be affected by the beam energy and current; the best value achieved was 10−2 Ω cm.

Current status of direct growth of CdTe and HgCdTe on silicon by molecular‐beam epitaxy

Abstract: CdTe and HgCdTe can be grown directly on Si(100) substrates by molecular‐beam epitaxy. The layers grow in the (111)B orientation. Single domain films are always obtained on Si(100) 8° off toward [011], whereas single and double domain films were obtained on nominal Si(100). A possible reason for the formation of these domains is discussed based on a microscopic model of the CdTe/Si interface. The structural quality of the layers is determined by double crystal x‐ray rocking curves. The narrowest rocking curves are obtained on single‐domain films grown on nominal Si(100) substrates; a full width at half‐maximum (FWHM) of only 230 arcsec was measured, compared to 460 arcsec on the best layer with two domains. For HgCdTe layers grown on CdTe/Si, rocking curves with 110 arcsec FWHM were measured; these layers are n‐type with electron mobilities above 5×104 cm2 V−1 s−1 at 23 K for a Cd mol % of 26%.

Analysis of molecular-beam epitaxial growth of InAs on GaAs(100) by reflection anisotropy spectroscopy

Abstract: The molecular‐beam epitaxial growth of InAs on GaAs(100) was investigated in situ using reflection anisotropy spectroscopy (RAS) and simultaneously reflection high‐energy electron diffraction. The RAS spectra of the GaAs c(4×4) and (2×4) and the InAs (4×2) and (2×4) reconstructions are reported. During InAs deposition, the RAS signal shows significant changes for InAs coverages as low as 1/6 of a monolayer. At this coverage surface reconstructions are responsible for the signal variation. For InAs coverages larger than four monolayers, the RAS signal is essentially determined by the anisotropic roughness of the three‐dimensional growing surface. This is verified using a three‐layer model which gives an excellent description of the experimental spectra at large coverages.

The growth and characterization of Si1−yCy alloys on Si(001) substrate

Abstract: We have prepared Si1−yCy alloy layers on Si (001) substrates using solid‐source molecular‐beam epitaxy. The lattice mismatch between diamond and Si is about 50%. Thus, a Si1−yCy (y=0.02) alloy has a mismatch of about 1% with respect to Si assuming Vegard’s law. Transmission electron microscopy (TEM) shows the layers to be pseudomorphic. Growth temperatures between Tg=500–550 °C are suitable for Si1−yCy layers with y≤0.05 for a growth rate of about 0.2 nm/s. Raman spectra show a distinct phonon mode at 600 cm−1, which is characteristic of substitutional carbon in Si. The Raman spectra show no evidence of silicon carbide precipitates, nor are precipitates observed in the cross‐sectional TEM micrographs. This is consistent with the lattice constant measurements by x‐ray diffraction. Amorphous growth occurs for lower substrate temperatures or significantly higher carbon concentration. That means, with increasing y in the Si1−yCy alloy layer the substrate temperature must be increased moderately. We have also ...

Cascade mixing limitations in sputter profiling

Abstract: The most fundamental physical processes which limit the depth resolution achieved in depth profiling by sputtering and surface analysis techniques are surface microroughening and atomic mixing in the collisional cascade. A survey of theoretical modeling of cascade mixing and its effect on the shape of measured profiles is presented. In particular, diffusion type models show reasonable agreement with recent experimental results of secondary ion mass spectroscopy and Auger electron spectroscopy profiles on delta function marker layers and on multilayer sandwich structures. The mixing range is related to the range of the primary ions and determines the depth resolution. Minimum values obtained under optimized sputtering conditions are of the order of 1 nm. Depending on the gradient of the true in‐depth distribution of composition, deconvolution procedures may become necessary to disclose the latter. Because sputtering is based on cascade mixing, the ultimate achievable resolution in depth profiling is limited by this effect.