R. J. Markunas

Single‐crystal diamond plate liftoff achieved by ion implantation and subsequent annealing

We describe a new method for removing thin, large area sheets of diamond from bulk or homoepitaxial diamond crystals. This method consists of an ion implantation step, followed by a selective etching procedure. High energy (4–5 MeV) implantation of carbon or oxygen ions creates a well‐defined layer of damaged diamond that is buried at a controlled depth below the surface. For C implantations, this layer is graphitized by annealing in vacuum, and then etched in either an acid solution, or by heating at 550–600 °C in oxygen. This process successfully lifts off the diamond plate above the graphite layer. For O implantations of a suitable dose (3×1017 cm−2 or greater), the liftoff is achieved by annealing in vacuum or flowing oxygen. In this case, the O required for etching of the graphitic layer is also supplied internally by the implantation. This liftoff method, combined with well‐established homoepitaxial growth processes, has considerable potential for the fabrication of large area single crystalline dia...

Remote plasma‐enhanced chemical‐vapor deposition of epitaxial Ge films

Epitaxial Ge films have been deposited at 300 °C using a remote plasma‐enhanced chemical‐vapor deposition technique where metastable He atoms flow downstream from the plasma region to dissociate GeH4 molecules into deposition precursor species. Ge epitaxy is demonstrated on Ge(111), Si(100), and GaAs(111)Ga face substrates. An in situ cleaning process that involves a moderate thermal bake at 300 °C and a hydrogen plasma etch of the native oxides is integral to the process. Reflection high‐energy electron diffraction is used to examine surface quality just prior to and after deposition. Uniform integral order diffraction streaks and fractional order reconstruction features observed from the Ge epilayers indicate that high quality Ge epitaxial layers can be grown using remote plasma‐enhanced chemical‐vapor deposition.

On the feasibility of growing dilute CxSi1−x epitaxial alloys

Dilute CxSi1−x epitaxial films have been grown on Si(100) by remote plasma‐enhanced chemical vapor deposition. Carbon concentrations of ∼3 at.% have been achieved at a growth temperature of 725 °C. No evidence for the formation or precipitation of SiC was found using x‐ray diffraction and transmission electron microscopy.

Direct deposition of polycrystalline diamond films on Si(100) without surface pretreatment

Dense nucleation of small‐grain polycrystalline diamond films on Si(100) substrates has been accomplished without the use of any surface pretreatment such as abrasive diamond scratching, surface oil treatments, or diamond‐like carbon predeposition. Diamond depositions occurred in a low‐pressure rf plasma‐assisted chemical vapor deposition system using mixtures of CF4 and H2. Films deposited at 5 Torr and 850 °C on as‐received silicon wafers show dense nucleation, well‐defined facets, and crystallites which ranged in size from 500 to 10 000 A. X‐ray photoelectron spectroscopy and electron energy loss show the films to be diamond with no major impurity and no detectable graphitic component. Raman spectroscopy shows a pronounced 1332 cm−1 line accompanied with a broad band centered about 1500 cm−1.

Low interface state density SiO2 deposited at 300 °C by remote plasma‐enhanced chemical vapor deposition on reconstructed Si surfaces

A 300 °C process has been used to deposit high‐quality SiO2 on Si. The process is based on remote plasma‐enhanced chemical vapor deposition. In this process excited species from a remote oxygen plasma interact with silane in the deposition zone. A hydrogen plasma is used to clean the silicon surface in situ just prior to deposition. After a 400 °C post‐metallization anneal, interface‐state densities as low as 3.7×1010 cm−2 eV−1 were measured with a fixed charge density of 2×1011 cm−2. The films exhibited good breakdown integrity, sustaining fields of 9–10 MV cm−1. The Si/SiO2 interface‐state density directly correlates with the quality of reflection high‐energy electron diffraction patterns from the silicon surface just prior to oxide deposition.

In situ cleaning of GaAs surfaces using hydrogen dissociated with a remote noble-gas discharge

In situ cleaning of GaAs surfaces has been achieved at 350 °C with a novel technique employing hydrogen that is excited and dissociated using a remote Ar discharge. Reconstructed surfaces characteristic of clean, As‐stabilized GaAs surfaces have been observed with reflection high‐energy electron diffraction following the cleaning treatment. Auger electron spectroscopy analyses confirm that such a treatment removes both carbon and oxygen contamination from the surface. X‐ray photoelectron spectroscopy shows the removal of oxygen bonded to both Ga and As on the surface. Emission spectroscopy shows evidence of excited molecular and atomic hydrogen with the downstream‐excitation process.

Low‐defect‐density germanium on silicon obtained by a novel growth phenomenon

Heteroepitaxial Ge on Si has been grown using molecular beam epitaxy at a Si substrate temperature of 900 °C. Electron microscopy results reveal a highly faceted interface, indicating localized Ge melting and subsequent local alloying with Si. Furthermore, this phenomenon is associated with extensive threading dislocation confinement near the Ge/Si interface. Etch pit density measurements obtained on Ge heteroepitaxial films that have undergone interfacial melting are as low as 105 cm−2.

The role of atomic hydrogen and its influence on the enhancement of secondary electron emission from C(001) surfaces

The role of chemisorbed hydrogen in the enhancement of low-energy electron emission from natural type IIb C(001) diamond surfaces has been investigated. A hydrogen induced low-energy emission peak, whose intensity was found to be a linear function of surface coverage, was observed. The direct observation of emission from vacuum level states in the photoemission spectra has determined a negative electron affinity of ∼0.4 eV for the hydrogenated C(001)-1×1 surface. Constant initial states photoemission has unambiguously identified the electron emission process with the escape of electrons from bulk electron states at the conduction-band minimum.

SECONDARY ELECTRON EMISSION ENHANCEMENT AND DEFECT CONTRAST FROM DIAMOND FOLLOWING EXPOSURE TO ATOMIC HYDROGEN

Polished nominal (100) surfaces of four types of diamonds were exposed to atomic hydrogen by hot filament cracking of H2 gas or by immersion in a H2 plasma discharge. Both types IIa and IIb (100) diamond surfaces exhibited the following characteristic changes: (a) secondary electron (SE) yield increased by a factor of ∼30 as measured in a scanning electron microscope (SEM), (b) near‐surface, nontopographical defects were observable directly using the conventional SE mode of the SEM, (c) surface conductance increased by up to 10 orders of magnitude. These changes were observed only weakly in nitrogen‐containing types Ia and Ib diamonds.

Demonstration of an n-channel inversion mode GaAs MISFET

Summary form only given. An operational GaAs inversion mode n-channel MISFET has been demonstrated using a composite SiO/sub 2/ (15 nm)/Si (1 nm)/GaAs structure. This result is based on an in situ hydrogen cleaning process (used to prepare the GaAs surface just prior to the Si-SiO/sub 2/ deposition), a low-temperature pseudomorphic Si deposition process, and a low-temperature high-quality SiO/sub 2/ deposition process, all performed sequentially in an ultrahigh-vacuum/load locked system. The first working devices exhibit a DC transconductance of 0.26 mS/mm at a gate length and width of 2 mu m and 50 mu m, respectively. Capacitance-voltage analysis of MIS capacitors on chip with the transistors indicates that the midgap electron trap density is on the order of 4*10/sup 11/ cm/sup -2/.<<ETX>>