Peter P. Pronko

Ellipsometric measurements of molecular‐beam‐epitaxy‐grown semiconductor multilayer thicknesses: A comparative study

Variable angle of incidence spectroscopic ellipsometry, cross‐sectional transmission electron microscopy, and Rutherford backscattering are used to measure heterojunction layer thicknesses in the same AlGaAs/GaAs sample. All three techniques yield the same thickness values within error limits. Two additional samples were implanted with 750‐keV Ga ions to fluences of 5×1015 and 1016 cm−2, respectively, and results of diagnostics measurements by the three techniques compared. The three techniques are found to complement each other in providing useful information.

Roughness studies of ion beam processed molybdenum surfaces

Mechanically polished molybdenum samples have been irradiated with 150 keV molybdenum ions at fluences from zero to 16×1015 ions/cm2 to study the effects on surface smoothing. Both fluence and substrate temperature during irradiation (25, 250, and 500 °C) had considerable effects on the optical properties. Ellipsometry, profilometry, and Nomarski photography were used to characterize the surfaces. Multiple wavelength, multiple angle of incidence ellipsometry results were analyzed using effective medium approximation models, with molybdenum, molybdenum oxide, and voids as the principal constituents. Generally, we find that the reflectance calculated from the ellipsometric measurements increases continuously as a function of fluence. However, for high substrate temperature and short wavelength the reflectance as a function of fluence reaches a maximum and then decreases. Effective medium calculations indicate that there is a corresponding change in the surface roughness with fluence, and that effects due to...

Atomic and carrier profiles of 1‐, 2‐, 4‐, and 6‐MeV 30Si implanted into GaAs

30Si has been implanted in GaAs at energies of 1, 2, 4, and 6 MeV. We have measured atomic concentration profiles using secondary ion mass spectroscopy (SIMS) and carrier concentration profiles using an electrolytic capacitance‐voltage procedure. Theoretical atomic profiles have been calculated using the computer code TRIM‐86. The range statistics and profile shape factors: Rm, Rp, ΔRp, skewness (γ1), kurtosis (β2), and maximum Si density (Nmax) have been determined from the SIMS data. The first two moments (Rp and ΔRp) were also obtained from the carrier profiles and the theoretical profiles. The range and standard deviation obtained by the separate techniques have a maximum difference of only 15%, and the difference is usually less than 10%. This is less than the mutual experimental uncertainty of 17%. The samples were activated using a furnace anneal (800 °C, 15 min) with a Si3N4 cap and using rapid thermal anneal (1000 °C, 10 s) with and without a cap. No redistribution of Si was observed for any of t...

Study of Mo‐, Au‐, and Ni‐implanted molybdenum laser mirrors by multiple angle of incidence spectroscopic ellipsometry

Multiple angle of incidence spectroscopic ellipsometric data show that implantation of 150‐keV molybdenum ions into polished molybdenum laser mirrors causes microscopic surface smoothing, and that most of the microscopic roughness is removed by a fluence of 5×1015 cm−2. Implantation of Au at 1 MeV significantly increases the microscopic roughness, and also changes the bulk optical properties. 3‐MeV Ni ion implantation causes only small changes in the surface and bulk properties. A dielectric film, probably a hydrocarbon, is found to condense on the mirrors in a laboratory atmosphere.

Thermal stability of electrically active dopants in laser annealed silicon films

Single crystal Si wafers and polycrystalline Si films on Si3N4 have been implanted with large doses (1×1015/cm2–4×1016/cm2) of P or As and laser annealed with either a cw or pulsed laser. The samples were then subjected to thermal anneals between 450 and 900 °C to determine the thermally stable dopant concentration for each sample. Sheet resistance and Hall measurements have been used to measure the electrical properties in each case. SIMS, RBS, and TEM have been used to measure atomic profiles, As substitutionality and residual defects after laser and thermal annealing. In each case the maximum electrically active dopant concentration achieved by laser annealing decreased after a 700–800 °C thermal anneal.

Ion beam smoothing of metallic mirrors

Abstract The implantation of 150 keV molybdenum ions into molybdenum mirrors and 400 keV silver or copper ions into copper mirrors is found to increase the reflectivity of these mirrors. Analysis of ellipsometric data from these samples using the Bruggeman effective medium approximation demonstrates that the change is due to smoothing of the surface. The improvement reaches a maximum as a function of fluence and then declines as the surface is roughened through sputter-induced topography. The smoothing effect appears to be dependent on elastic energy deposition in the vicinity of the surface. However, if the energy density at the surface is too high, such as with 1 MeV gold ions, then spike effects appears to roughen the surface before significant smoothing can take place. Rotating the samples in the ion beam does not affect the initial smoothing, or its decline, but delays the development of the visible roughening.

Atomic Profiles of High Energy (MeV) Si Implanted into GaAs

High energy Si implantation into GaAs is of interest for the fabrication of fully implanted monolithic microwave integrated circuits. 30 Si has been implanted into LEC GaAs at energies of 1, 2, 4, and 6 MeV. We have measured atomic concentration profiles using SIMS and carrier concentration profiles using an electrolytic CV procedure. Theoretical atomic profiles have been calculated using TRIM-86. Excellent SIMS dynamic range and low background ( 14 /cm 3 ) was achieved for the profiles by the use of 30 Si. The range statistics and profile shape factors: R m , R p , ΔR p , skewness (Y 1 ), kurtosis (B 2 ), and maximum Si density (N max ) have been determined from the SIMS data by applying a Pearson IV computer fitting routine. The first two moments (R p and ΔR p ) were also obtained from the carrier profiles and the theoretical profiles. The range and standard deviation obtained from each profile have a maximum difference of only 15%, and the difference is usually less than 10%. This is less than the mutual experimental uncertainty of 17%. The samples were activated using a furnace anneal (800°C, 15 min) with a Si 3 N 4 cap and using rapid thermal anneal (1000°C, 10s) with and without a Si 3 N 4 cap. No redistribution of Si was observed for any of the anneal conditions within experimental error.

Study of Ion Implanted Copper Laser Mirrors by Spectroscopic Ellipsometry

Implantation with 400 keV Ag or Cu ions improves the near-surface microstructural quality and reflectance of diamond turned and mechanically polished flat copper laser mirrors. Spectroscopic ellipsometry is sensitive to changes in either the microscopic surface roughness, or in the nearsurface substrate void fraction, and both parameters are observed to change upon implantation. Substrate density as a function of ion fluence peaks at about 5 × 10 15 cm -2 . Low energy (300 eV) Ar ion implantation can cause either a reduction or increase in microscopic surface roughness, depending on fluence.

The material state of ion‐implanted Cr in GaAs

Chromium‐implanted GaAs has been studied using 120 keV implants to fluence levels from 1×1014 to 5×1016 cm−2. The postannealed materials state has been examined using Rutherford backscattering spectrometry, proton‐induced x‐ray excitation, channeling, and transmission electron microscopy.Annealing was performed in flowing H2 at 900 C for 15 min under 85‐nm thick Si3N4dielectric caps. Various stages of precipitation were observed having structure and composition that depended on total implanted fluence. For the highest fluence, coarse nonuniform second‐phase precipitates were present with dimensions on the order of 50 to 100 nm. At lower fluences small defect cluster precipitates, with average diameters of 6 nm, were identified through black‐white contrast analysis. The relative fraction of precipitated Cr was 40% at 1×1015 cm−2 and decreased to 9% at 5×1014 cm−2. The volume concentration of implanted Cr that is retained in solid solution after annealing is estimated at 2×1018 cm−3. Channeling analysis suggests that these atoms are retained in nonunique interstitial or other nonsubstitutional positions.

Study of Mo, Au, and Ni implanted molybdenum laser mirrors by spectroscopic ellipsometry

The implantation of 150-keV molybdenum ions into polished molybdenum laser mirrors is found to increase the complex dielectric constant in the visible spectrum. Analysis using the Bruggeman effective medium approximation demonstrates that the increase is due to surface smoothing, and that the surface is made nearly atomically smooth by a fluence of 5 x 10/sup 15//cm/sup 2/. Implantation of Au at 1MeV caused considerable microscopic roughening, as well as a change in the bulk optical properties. 3-MeV Ni ion implantation caused only a slight surface roughening. A thin dielectric film (probably a hydrocarbon) is found to condense in a laboratory atmosphere, reducing the reflectivity, and is removable by rinsing with methanol and distilled water.