David I. Ma

Nitrogen depletion during oxidation in N2O

The incorporation of nitrogen in oxides has been studied after furnace oxidation in N2O at 900 °C. We observe that nitrogen is removed from the oxide bulk during oxidation in N2O, while simultaneously nitrogen is incorporated at the growing Si–SiO2 interface. This results suggests that nitrogen incorporation involves a dynamic equilibrium between competing processes which causes both nitrogen incorporation and depletion. A chemical model for nitrogen removal is proposed based on a reaction with NO. Reaction energies, estimated from semiempirical quantum‐mechanical calculations, support the proposed model.

Alternative approach to electroless Cu metallization of AlN by a nonaqueous polyol process

Cu metallization of AlN substrates was performed using a nonaqueous, electroless, alcohol based approach known as the polyol method. The concentration of Cu2O in the film depended on the orientation of the substrates during deposition. This approach is very attractive for metallizing electronic substrates which are susceptible to hydrolytic degradation.

The interaction of stoichiometry, mechanical stress, and interface trap density in LPCVD Si-rich SiNx;Si structures

Abstract Mechanical and electrical properties were correlated in LPCVD SiNx;Si structures through the characterization of six wafers patterned with MNS capacitors whose insulator films were deposited rich in Si under various processing conditions. The samples were measured for mechanical stress at the SiSiNx interface with X-ray diffraction. The deposited SiNx films were measured for stoichiometry by Rutherford backscattering spectroscopy. Low-temperature C-V measurements were used for the first time to estimate SiSiNx interface trap densities in the capacitors. The interface trap densities were confirmed with the aid of a model based on a numerical analysis of the capacitor small-signal response. The measurement results indicate that an increase in the Si/N ratio in the insulating films was accompanied by a decrease in the film tensile stress. Those SiNx films made sufficiently rich in Si were successfully deposited under compressive stress. Furthermore, a decrease in the magnitude of the stress was accompanied by a decrease in interface trap densities, suggesting that interfacial mechanical stress may be influential in the formation of SiSiNx interface traps. Interface trap densities were lowest in those structures whose insulating films were deposited under compression.

Electron-beam nanolithography, acid diffusion, and chemical kinetics in SAL-601

The work presents a unique investigation of the role of postexposure bake (PEB) on resist insolubility, PEB reaction kinetics, and the high resolution behavior of Microposit™ SAL-601. Patterns of 20–100 μm rectangles and single pass isolated lines were written on a JEOL JBX-5DII e-beam lithography system operated at 50 kV. The effects of PEB temperatures of 90–110 °C for periods of 1–11 min on resist insolubility and linewidth were examined. The samples were developed in MF-322 or acetone. The range of patterns allowed measurement of both the resist exposure curves and the line spread for each PEB condition. Insolubility in MF-322 can result from protection reactions and/or crosslinking reactions. Acetone insolubility, a characteristic of crosslinked resist, was observed at PEB temperatures of 100 °C and above. At 90 °C, acetone insolubility (crosslinking) was observed only after a PEB of 11 min. From the resist exposure curves for a sequence of PEB times, reaction orders for the PEB processes that led to...

Double‐crystal x‐ray topographic determination of local strain in metal‐oxide‐semiconductor device structures

A double‐crystal x‐ray topograph was used to determine local strain in metal‐oxide‐semiconductor (MOS) transistor test chips. The double‐crystal machine could sense strains as small as 10−6, with a spatial resolution of a few micrometers. Results indicate that two types of strain are present: local surface strain as well as the more familiar strain due to bulk deformation of the crystal. Both types of strain have been correlated with surface mobility changes in n‐channel metal‐oxide‐semiconductor (nMOS) transistors.

Characterization of thin boron‐doped silicon membranes by double‐crystal x‐ray topography

Heavily boron‐doped silicon transparent membranes and x‐ray masks were examined using double‐crystal x‐ray topography. The topographs revealed the strain distribution in two dimensional (2D) pattern. Slip bands and Frank–Read sources were observed. The stress variation across the membrane was confirmed using the Stoney’s stress analysis by laser beam reflecting technique. Surface strain versus bulk strain were also analyzed by choosing (224) and (115) reflecting planes. Deposition of patterns on a bare membrane did not alter the overall strain pattern of the membrane, which was apparently determined by the warpage of the silicon supporting ring. Local deformations associated with gold absorber features were visible and their associated strain fields were measured.

Planar, linear GaAs detector-amplifier array with an insulating AlGaAs spacing layer between the detector and transistor layers

Monolithic, high-speed planar, linear, parallel channel, ten-element GaAs detector-amplifier arrays with a 70- mu m detector center-to-center spacing have been fabricated using a GaAs-AlGaAs-GaAs epitaxial structure grown on semi-insulating GaAs. The AlGaAs layer provided excellent electrical isolation between the transistor and n-type photoconductor epitaxial layers. Rise and fall times of integrated detector-amplifier array channels of 650 ps and 1.1 ns, respectively, were measured at 0.84- mu m wavelength. The sensitivity of single, discrete, detector-amplifier channels was better than -34 dBm.<<ETX>>

High‐speed planar GaAs photoconductors with surface implant layers

Selective implantation of silicon into GaAs is demonstrated as a simple method for modifying the response characteristics of low‐doped planar GaAs photoconductors for optoelectronic circuits with varying requirements. Response times and sensitivities of the photoconductors were strongly dependent on the implantation dose and energy. Rise times and full width at half‐maximum (FWHM) values of devices receiving low‐dose implants were of the order of 40–150 ps. Rise times and FWHM values of devices which received higher dose implants were in the ranges 50–140 ps and 1–5 ns, respectively. The sensitivity of devices which received higher dose implants was about a factor of 100 (20 dB in optical power) greater than that of devices which received lower dose implants.

Proximity effect reduction in x‐ray mask making using thin silicon dioxide layers

A novel method is reported for reducing the proximity effect in high‐resolution electron beam patterning of high atomic number materials such as tungsten. The method involves interposing a thin (50–400 nm) layer of SiO2 between the resist and the underlying high‐Z substrate. Examples are shown in which gratings of 0.2 μm lines with a 0.5 μm period were written without proximity effect compensation. Optimal intermediate layer thickness for the best resolution of the gratings is determined to be 200 nm. A Monte Carlo model of electron scattering including inelastic processes has been implemented to interpret our experimental results. The model presented shows that having the low atomic number SiO2 layer between the resist and the tungsten prevents the fast secondary electrons being generated at the surface of the tungsten from propagating back into the resist, suggesting a mechanism for proximity effect reduction. The results presented here have important practical applications for x‐ray mask making.

Double-crystal X-ray topography characterization of an electrical-bias-induced stress variation in metal-oxide-semiconductor field effect transistors

n-channel metal-oxide-semiconductor (MOS) field effect transistors were biased under different operating conditions. Superficial silicon strain patterns were recorded by reflection mode double-crystal topography. Stress redistributions caused by various applied electrical field E biases were observed. A comparison of the electrical-field-induced stress and mechanically induced stress was made. On the basis of this result, the amount of bias-induced stress was measured. X-ray peak reflection intensity, the diffraction angle of this peak, and the full width at half-maximum of the X-ray double-crystal rocking curves under various biases were also analyzed. All of these measurements indicate that a weak piezoelectric effect exists in the superficial layers of MOS devices.