L.P. Allen

Craters on silicon surfaces created by gas cluster ion impacts

Atomic force microscopy (AFM) and high-resolution transmission electron microscope (HRTEM) cross section imaging of individual gas cluster ion impact craters on Si(100) and Si(111) substrate surfaces is examined. The comparison between 3 and 24 kV cluster impacts from Ar and O2 gas sources is shown. Results for low fluence (1010 ions/cm2) 24 kV Ar individual cluster impacts onto a Si(100) and Si(111) substrate surfaces are compared with hybrid molecular dynamics (HMD) simulations. A HMD method is used for modeling impacts of Arn (n=135, 225) clusters, with energies of 24–50 eV/atom, on Si(100) and Si(111) surfaces. On a Si(100), craters are nearly triangular in cross section, with the facets directed along the close-packed (111) planes. The Si(100) craters exhibit four-fold symmetry as imaged by cross-sectional HRTEM, and AFM top view, in agreement with modeling. In contrast, the shape of craters on a Si(111) shows a complicated six-pointed shape in the modeling, while AFM indicates three-fold symmetry of...

Surface processing with gas-cluster ions to improve giant magnetoresistance films

The reduction of roughness, without introducing damage, of thin-film surfaces in giant magnetoresistance (GMR) applications will be essential in the development of advanced devices. Tools and methods to accomplish this are limited at present. Gas-cluster ion beam (GCIB) technology shows promise as a dry, low-temperature process that can provide substantial improvement, and can be integrated into GMR-film deposition-and-etch tools. In this work, we describe recent GCIB technique developments and processes for tantalum, alumina, permalloy, and other relevant materials. With argon GCIB it is possible to reduce the roughness of many films to well below a nanometer (root-mean-square), with the roughness falling exponentially with cluster dose. Prototype magnetic films for evaluation were fabricated on GCIB-smoothed alumina gap layers. Transmission electron microscopy revealed changes in roughness and grain morphology that may be correlated with magnetic properties.

Crater formation and sputtering by cluster impacts

A multiscale computational model coupling atomistic molecular dynamics simulations with continuum elasticity was used for studying craters formed on Si surfaces by Ar cluster impacts, with energies of 20–50 eV/atom. The results were confirmed by atomic force microscopy/transmission electron microscopy. They show that on a Si (1 0 0), craters are nearly triangular in cross-section, with the facets directed along the close-packed (1 1 1) planes, and exhibit fourfold symmetry. The craters on Si (1 1 1) surface are well rounded in cross-section and the top-view shows a complicated sixfold or triangular image. The sputtering yield from Si surfaces bombarded with B10 cluster ions, with energy of 1–15 keV, was calculated.

Epitaxial growth on gas cluster ion-beam processed GaSb substrates using molecular-beam epitaxy

Chemical mechanical polished (CMP) (100) GaSb substrates were processed using gas cluster ion beams (GCIB) to improve surface smoothness, reduce subsurface damage, and produce a thermally desorbable oxide layer for molecular-beam epitaxy (MBE) overgrowth. In this article, we report the growth of GaSb/AlGaSb epilayers on GCIB processed GaSb substrates. The substrates were processed using either O2 or CF4/O2 as the gas cluster in a dual-energy recipe that included a moderate energy (10 keV) etch step followed by a low-energy (3 keV) smoothing step, with a relatively low total dose of 4×1015 ions/cm2. Half of each wafer was masked such that the epitaxial layers were grown on both CMP and GCIB polished surfaces. Atomic force microscopy showed the elimination of CMP surface scratches on the GCIB processed surfaces. X-ray photoelectron spectroscopy results indicate that the surface oxide composition and thickness can be engineered through the GCIB process recipes. AlGaSb marker layers were used to chart the evo...

Molecular beam epitaxy and morphological studies of homoepitaxial layers on chemical mechanical polished InSb(100) and InSb(111)B substrates

Noncontact atomic force microscopy (AFM) has been used to assess the surface morphology and structure of InSb homoepitaxial layers grown on chemical mechanical polished (CMP) InSb(100) and InSb(111)B surfaces. Although it is difficult to grow epilayers on highly conducting InSb substrates, this work demonstrates the ability to grow layers with an average roughness (Ra) of 5.7A on 2×1018 n-type InSb(100) surfaces. Furthermore on 7×1014 n-type InSb(111)B surfaces, extremely flat layers with Ra’s of approximately 1.7A were grown. Thermal x-ray photoelectron spectroscopy was implemented to analyze surface oxide desorption on the CMP prepared “epiready” wafers. Sb to In flux ratio and substrate deposition temperature are critical in obtaining high quality epitaxial material. For the InSb(100) surfaces, an Sb∕In flux ratio of 1.5:1, a substrate temperature of 380°C, and a background pressure of 1×10−10Torr produced smooth surfaces. For InSb(111)B surfaces, a ratio of 7:1 and a substrate temperature of 380°C at ...

Fundamental material analysis and SIMOX improvement as a function of independent implant parameter control

Until recently, implanted material fabrication incorporated inherently coupled parameters of the selected species implant. With the advent of decoupled implant parameters, first and second order material quality influences can be determined and applied towards material improvements. This paper reports on the fundamental material analysis and SIMOX quality as a function of independently controlled wafer temperature, energy, and beam current. Their influence on the microstructure and electrical behavior of single implant SIMOX material has been investigated for a resulting improvement in the silicon/buried oxide interface and an understanding of dislocation reduction and buried oxide improvement mechanisms.

Gas Cluster Ion Beam Processing of GaSb and InSb Surfaces

Gas Cluster Ion Beam (GCIB) processing has recently emerged as a novel surface smoothing technique to improve the finish of chemical-mechanical polished (CMP) GaSb (100) and InSb (111) wafers. This technique is capable of improving the smoothness CMP surfaces and simultaneously producing a thin desorbable oxide layer for molecular beam epitaxial growth. By implementing recipes with specific gas mixtures, cluster energy sequences, and doses, an engineered oxide can be produced. Using GaSb wafers with a high quality CMP finish, we have demonstrated surface smoothing of GaSb by reducing the average roughness from 2.8A to 1.7A using a dual energy CF 4 /O 2 -GCIB process with a total charge fluence of 4×10 15 ions/cm 2 . For the first time, a GCIB grown oxide layer that is comprised of mostly gallium oxides which desorbed at 530°C in our molecular beam epitaxy system is reported, after which GaSb/AlGaSb epilayers have been successfully grown. Using InSb, we successfully demonstrated substrate smoothing by reducing the average roughness from 2.5A to 1.6A using a triple energy O 2 -GCIB process with a charge fluence 9×10 15 ions/cm 2 . In order to further demonstrate the ability of GCIB to smooth InSb surfaces, sharp ∼900nm high tips have been formed on a poorly mechanically polished InSb (111)A wafer and subsequently reduced to a height of ∼100nm, an improvement by a factor of eight, using a triple energy SF 6 /O 2 -GCIB process with a total charge fluence of 6×10 16 ions/cm 3 .

Gas cluster ion beam processing of SOI surfaces for improved gate oxide integrity

In this study, SOI substrates were delivered to Honeywell SSEC in order to assess the effectiveness of a gas cluster ion beam smoothing process on the gate oxide integrity (GOI) of silicon-on-insulator (SOI) wafers using a fast turn around GOI test process.

Effect of varying implant energy and dose on the SIMOX microstructure

SIMOX (Separation by IMplantation of OXygen) is one of the leading SOI (silicon an insulator) technologies. SOI materials have received considerable attention for their potential use in deep submicron device technology, and low power, low voltage and high density applications. The quality of the Si overlayer and the buried oxide (BOX) needs further improvement to avoid possible deleterious effects on devices. The main defects in the Si overlayer are cavities, stacking faults and dislocation half loops in the as implanted state, and threading dislocations in the annealed state. Si islands in the BOX degrade its dielectric property and processing conditions need to be further improved to minimize these defects in the BOX, especially for low dose SIMOX. Finally, the quality of the Si surface and top Si/BOX interface are of importance for device grade SIMOX. A comprehensive study of all the above microstructural features have been done as a function of varying the implant energy and dose and the results compared in this report.

Independent implant parameter effects on SIMOX SOI dislocation formation

Abstract Separation by implanted oxygen (SIMOX) material has proven to provide an extended temperature range (up to 500 °C) of operation for partially depleted silicon-on-insulator (SOI) test structures and product circuits in both transportation and communication applications. Such high temperature use is possible due to the built-in dielectric isolation which eliminates the isolation junction and its associated leakage. In order to further improve high temperature performance, material quality must be ever improving. This study examines the independent implant parameter effects of implant energy, implant temperature, and beam current density on the silicon threading dislocation density in standard and thin buried oxide (BOX) SIMOX material. We have found that increased implant energies and a slightly lower beam current will improve the dislocation density by at least an order of magnitude. The kinetics of vacancy formation as it relates to the above parameters are presented.