R. Asahi

Anisotropic etching of silicon in TMAH solutions

Abstract Detailed characteristics of tetramethyl ammonium hydroxide (TMAH, (CH3)4NOH) as silicon anisotropic etching solutions with various concentrations from 5 to 40 wt.% and temperatures from 60 to 90 °C have been studied. The etch rates of (100) and (110) crystal planes decrease with increasing concentration. The etched (100) planes are covered by pyramidal hillocks below 15 wt.%, but very smooth surfaces are obtained above 22 wt.%. Etch rates of 1.0 μ/min for the (100) plane and 1.4 μ/min for the (110) plane at 90 °C are obtained using a 22 wt.% solution. The etch-rate ratio of (111)/(100) varies from 0.02 to 0.08. The etch rate of thermally oxidized SiO2 is almost four orders of magnitude lower than that for (100) and (110) planes. The etch rates of aluminium are reduced by dissolving silicon in TMAH solution. Etch-stop techniques using a heavily boron-doped layer or p—n junction prove to be applicable to TMAH solutions.

Micromachined sensors using polysilicon sacrificial layer etching technology

Sensor assembly is one of the key technologies to improve the cost performance of silicon sensors. As a technology to achieve this aim, polysilicon sacrificial layer etching technology is presented. As its applications, a microdiaphragm pressure sensor with a reference pressure chamber and an integrated pyroelectric infrared sensor with a thermal isolated structure are also presented. Fabrication of a micro optical chopper is shown, and the future style of sensor devices is proposed.<<ETX>>

Accurate first-principles detailed-balance determination of Auger recombination and impact ionization rates in semiconductors

The technologically important prediction of Auger recombination lifetimes in semiconductors is addressed by means of a fully first-principles formalism, based on precise energy bands and wave functions provided by the full-potential linearized augmented plane wave code. The minority carrier Auger lifetime is determined by two related approaches: (i) a direct evaluation within Fermis golden rule, and (ii) an indirect evaluation, based on a detailed balance formulation combining Auger recombination and its inverse process, impact ionization, in a unified framework. Lifetimes determined with the direct and indirect methods show excellent consistency between them (i) for n-doped GaAs and (ii) with measured values for GaAs and InGaAs. This indicates the computational formalism as a new sensitive tool for use in materials performance optimization.

Anisotropic etching of silicon in (CH/sub 3/)/sub 4/NOH solutions

Detailed characteristics of tetramethyl ammoniumhydroxide, (CH/sub 3/)/sub 4/NOH, as silicon anisotropic etching solutions with various concentrations from 5 to 40 wt.% have been studied. The etch rates of

Infrared linear image sensor using a poly-Si pn junction diode array

Abstract An IR linear image sensor using a poly-Si pn junction diode array has been developed. The poly-Si pn junction diode detector is supported on a thin insulating membrane formed using anisotropic etching and a sacrificial poly-Si etching settler. The fabrication of this linear image sensor allows compatible integration of both IR detectors and conventional Si-IC processes. This sensor consists of 16 bit elements, each of 400 μm × 400 μm dimensions, and overall area 10.0 × 2.5 mm2. We obtained, at room temperature, the values Rv = 50 V W and D ∗ = 6.0 × 10 5 cm Hz 1 2 /W .

Impact Ionization in GaAs within A Screened Exchange Density Functional Formalism

We present the results of a fully first-principles calculation of impact ionization rates in GaAs within the density functional theory formalism, using a screened-exchange approach and the highly accurate all-electron full-potential linearized augmented plane wave (FLAPW) method. The calculated impact ionization rates show a marked orientation dependence in k space, indicating the strong restrictions imposed by the conservation of energy and momentum. This anisotropy diminishes as the impacting electron energy increases. A Keldysh type fit performed on the energy-dependent rate shows a rather soft edge and a threshold energy greater than the direct band gap. The consistency with available Monte Carlo and empirical pseudopotential calculations shows the reliability of our approach and paves the way to ab-initio calculations of pair production rates in new and more complex materials.