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We present a fabrication process for a family of thermal microsensors and microactuators based on a porous silicon sacrificial layer technology. In contrast to previous work on porous-silicon-based micromachining processes, our process is modularized into a complementary metal-oxide semiconductor (CMOS) compatible front-end and a sensor- or actuator-specific back-end module. The front-end module yields silicon hotplate structures which can be fabricated in typical CMOS foundries. Such hotplates are characterized by high mechanical strength and good thermal insulation. High levels of thermal insulation are attained by employing extremely deep sacrificial layers approaching the wafer thickness. We show that different kinds of thermal microsensors and microactuators can be produced using identical front-end modules. The adaptation of the microstructures to different application needs can be performed in a small number of sensor- or actuator-specific back-end processes. We propose that such modularization schemes allow small- and medium-sized companies, with specialized application know-how and access to limited-size markets, to benefit from the mass fabrication capabilities of modern silicon foundries.

This paper reports on the development of a dry etching based HARMS-Technology which will offer the potential to manufacture micro-engines, micro-turbines, micro-sensors, micro-actuators, and electronic circuits onto a single silicon IC chip. This technology is based on the highly anisotropic and selective dry etching of Si-monocrystals. The suitability of reactive ion etching for the fabrication of micro electro mechanical systems (MEMS) has been evaluated by characterising the change of lateral dimensions vs. depth in etching deep structures in silicon. Fluorine, chlorine and bromine containing gases have provided the basis for this investigation. A conventional planar RIE (Reactive Ion Etching) reactor has been used, in some cases with magnetic field enhancement or ICP (Inductive Coupled Plasma) Source and low substrate temperature. For reactive ion etching based on Cl2 or Cl2/HBr plasma a slightly “positive” (top wider than bottom) slope is achieved when etching structures with a depth of several 10 μm, whereas a “negative” slope is obtained when etching with an SF6/CCl2F2 based plasma. Pattern transfer with vertical walls is obtained for reactive ion etching based on SF6 (with O2 added) when maintaining the substrate at low temperature (in range ≈−100 °C). Further optimisation of plasma chemistries and reactive ion etching procedures should result in runouts in the order or 0.1 μm/100 μm depth in Si as well as in organic materials. Etching processes for HARMST is demonstrated in the realisation in Si microturbine. Axes or stators (nonmoving parts) are etched into the initial Si-wafer. The movable parts (rotors, beams, etc.) are prepared from electro-chemically etched Si-membranes with defined thicknesses that, all movable parts are created lithographically on the SiNxOy surface. This is followed by dry etching the mono-crystalline Si-membrane down to the SiNxOy sacrificial layer on the back side of the membrane by an RIE-process. The wafer with the movable parts is flipped onto the wafer with the already etched axis and then positioned and centred. The SiNxOy-sacrificial layer is then dissolved by a chemical wet or vapour etch process. Subsequent bonding with a Pyrex glass wafer seals the parts.

The properties of a Pd—Au complex in n-type Si are investigated by DLTFS (deep level transient Fourier spectroscopy) techniques. In n-type Si the energy level of the Pd—Au complex is slightly shifted with isochronal annealing and does not display stable properties. The defect reaction of Pd—Au is explained by an “enhanced kick-out” mechanism represented by the reaction equation Aui + Pds Aus + Pdi, where interstitially diffusing gold replaces substitutional palladium. This reaction is similar to the Au—Rh defect reaction. The results of the investigations of the properties of the Pd—Au complex in p-type Si will be published later. Die elektrischen Eigenschaften des Pd—Au-Komplexes in n-Si werden mit dem DLTFS (deep level transient Fourier spectroscopy) Verfahren untersucht. Die Energieniveaus dieses Komplexes in n-Si verschieben sich bei Temperung und sind bei hohen Temperaturen nicht stabil. Die Pd—Au-Reaktion wird durch den “enhanced kick-out” Mechanismus erklart, der durch die Reaktionsgleichung Aui + Pds Aus + Pdi beschrieben wird, wobei interstitiell diffundierendes Gold substitutionelles Pd ersetzt. Diese Reaktion entspricht der Au—Rh-Reaktion. Die Ergebnisse der elektrischen Eigenschaften des Pd—Au-Komplexes in p-Si werden demnachst veroffentlicht.

Metalorganic vapour-phase epitaxy (MOVPE) growth experiments for GaAs and (AlGa)As have been performed as a function of growth temperature and V/III ratio using the new alternative precursor diethyl-tert-butylarsin (DEtBAs) in combination with trimethylgallium (TMGa) and trimethylaluminium (TMAl). The incorporation of deep traps has been investigated by means of photoluminescence (PL) and deep level transient Fourier spectroscopy (DLTFS). In (AlGa)As layers grown with DEtBAs a drastic reduction of the deep broad band luminescence between 1.5 and 2 eV is observed in dependence of the growth conditions. A probably deep complex defect involving an As vacancy is observed in (AlGa)As layers grown with DEtBAs. In GaAs layers grown with DEtBas or AsH 3 the dominant deep trap is the EL2 defect. Deep level photoluminescence studies show a reduced incorporation of the EL2 defect as compared to AsH 3 grown layers, due to the smaller V/III ratio. The obtained low deep defect concentration in particular for GaAs layers underlines the great potential of the model precursor DEtBAs as substitute for the highly toxic AsH 3 in MOVPE

The performance of the AZ PF 514 positive resist in single-layer electron-beam lithography (EBL) and reactive ion etching (RIE) has been investigated. The fabrication possibilities of silicon micromechanical parts and structures with nanometer details are presented. The basic lithographic and pattern transfer properties are discussed.

A novel type of micromachined thermal mass flow sensor has been developed which is characterised by enhanced mechanical and thermal stability. For its realisation /spl beta/-SiC films were heteroepitaxially deposited onto pre-processed silicon wafers. After structuring the surface /spl beta/-SiC films to form heater and temperature sensing elements, porous silicon was formed in predetermined parts of the silicon substrate to form flow channels. The so formed devices are able to detect bidirectional flows of air with a temporal resolution of 2-3 msec. Due to the excellent mechanical and thermal stability of the /spl beta/-SiC heater and temperature sensing elements, the devices are able to sustain extremely harsh environmental and operating conditions: firstly, flows of pressurised air could be sustained without inflicting mechanical damage to the micromachined /spl beta/-SiC bridges, secondly, several hours of thermal cleaning at white glow in ambient air could be endured before breakages due to thermal oxidation occurred.

This work presents the detailed description of the formation process of the silicon microreactors and micromechanical structures which will dominate the near future. The description is based mainly on the author’s experience and includes a description of the dry etching of silicon by means of different halogen plasmas. The well established methods of microsystem technology allow the cheap and fast production of silicon based microtools in large numbers via batch processing.

A new silicon based, planar hybrid technology is being developed to address limitations associated with packaging and interconnections. The approach combines the advantages of both hybrid and monolithic technologies. Microwave transistor chips (e.g. GaAs FETs) are glued with an epoxy resin in openings micromachined in a high resistivity silicon substrate with a vertical precision of better than 2 ?m and lateral tolerances less than 10 ?m. Air bridge technology and thin film techniques are then used to provide the necessary interconnections. Preliminary results show very promising high frequency properties of this assembly.

Scanning force microscopy (SFM), operated in the attractive imaging mode, enables the precise measurement of the force between tip and sample over a tip–sample distance ranging from contact to tens of nanometers. The basic long range interactions (>1 nm: i.e., hydrodynamic, electrostatic, van der Waals, and capillary forces) between tip and sample have been measured and will be discussed. Each force leads to a different mode of operation in profiling samples. The most critical part of the SFM is the force sensor. Exact knowledge of the sensor properties is required for the interpretation of SFM measurements. We have used micromachined silicon sensors consisting of a monolithic silicon cantilever with integrated silicon tip and have performed a detailed characterization of the tip geometry and resonance properties. Examples of surface images on different samples (conductors, insulators and biological materials) and structures, ranging from atomic steps up to several microns high features, have been investi...

The value of the capture rate cn and the capture cross section σn of the gold acceptor level is determined from single injection SCLC measurements at high resistivity Au-compensated n+–i–n+-Si samples. By means of a single and double pulse method the time dependence of the current is measured for the capture and reemission of electrons by the Au-acceptor level. The capture and emission time constant τ and τe were calculated according to the SRH model. From the temperature dependence of τe the activation energy Ec–EAu was determined. The obtained value of cn agrees quite well with that given by Bemski whereas the value given by Fairfield and Gokhale cannot be confirmed. The value of cn calculated from the emission rate e given by Sah is too large by a factor of about four. An hochohmigen goldkompensierten n+–i–n+-Siliziumproben wurden der Einfangs-koeffizient cn und der Wirkungsquerschnitt σn des Goldakzeptorniveaus bestimmt. Mit Hilfe einer Einfach- und einer Doppelimpulsmesmethode wurde der Strom-Zeitverlauf fur den Einfang und die Reemission von Elektronen durch das Akzeptorniveau gemessen. Ausgehend vom Modell von Shockley, Read und Hall wurde der Strom-Zeitverlauf berechnet und aus dem Vergleich mit dem Experiment die Einfang- und Emissionszeit-konstante bestimmt. Aus der Temperaturabhangigkeit der Emissionszeitkonstanten wurde die Aktivierungsenergie Ec–EAu bestimmt. Der ermittelte Wert fur cn stimmt recht gut mit dem von Bemski angegebenen uberein, last sich jedoch nicht mit dem von Fairfield und Gokhale bestimmten in Einklang bringen. Aus dem von Sah angegebenen Wert fur e ergibt sich ein um den Faktor vier groserer Wert fur cn.

Theoretical and experimental investigations on the small signal behavior of sclc-diodes containing deep levels were performed. The experimental results were obtained from high resistivity Au-compensated n + in + -silicon samples. The measurements of the frequency dependent conductance and capacitance are consistent with theory up to frequencies ω T >1. From the bias dependence of the capacitance a method is deduced to determine the capture time constant easily and with high accuracy and, if the trap concentration is already known, the capture cross section. The value obtained for the gold acceptor level agrees well with that determined by means of transient current measurements.

DLTS measurements on the gold donoe and acceptor level in p-type silicon and reported. From the experimental data it must be concluded that the gold donor and the acceptor level are caused by the same defect, that the acceptor level lying 0.546eV below the conduction band is temperature independently pinned to the conduction band and that the hole capture cross section of the acceptor level P A is temperature independent in the measured range of 215 to 345 K.

The diffusion of B and As from polycrystalline Si into single‐crystal Si during rapid optical annealing (ROA) has been investigated. Samples were characterized by secondary ion mass spectrometry, transmission electron microscopy, and sheet resistance measurements. It is demonstrated that very shallow diffusion profiles in the single‐crystal Si can be formed by ROA. At 1050 °C/5 s, for instance, a junction depth of ∼35 nm is obtained for As diffusion. The effect of polycrystalline Si/mono‐Si interface treatment on the dopant diffusion and the polycrystalline Si grain structure will be discussed.

The parameters of the gold donor level inp-type silicon are determined from the temperature dependence of the free carrier concentration and from DLTS measurements. The entropy-factorX T is determined to be 20±2. In addition, the capture cross-section for holes σ p =5.5×10−15 cm2 and the reaction enthalpyH T −H v =0.35eV for the exchange of holes between the gold donor level and the valence band are obtained in the present investigation.

The temperature independence of the capture cross-section of the neutral Au-acceptor level for electrons in silicon, σn, in the range of 172 to 316 K is found. The measurements were performed at high-resistivity, Au-compensated single-injection SCLC diodes by means of a pulse and a small-signal capacitance method. In der vorliegenden Arbeit wird die Temperaturunabhangigkeit des Wirkungsquerschnitts σn des neutralen Au-Akzeptorniveaus fur Elektronen in Silizium im Temperaturbereich 172 bis 316 K nachgewiesen. Die Messungen wurden an hochohmigen Au-kompensierten Einfachinjektions-SCLC-Dioden mit Hilfe einer Puls- und einer Kleinsignal-Kapazitatsmethode durchgefuhrt.

Calculations have been made of dc I‐V characteristics of long p+‐i‐n+ diodes with deep levels showing a negative differential resistance region. The influence of the recombination center data, especially of the capture coefficients of both electrons and holes, cn and c−p, is discussed. The calculations show that cn only influences the high injection regime and the minimum voltage, whereas c−p only influences the prebreakdown region and the breakdown voltage; thus a new method arises to determine cn and c−p in the same sample. These results are confirmed in silicon p+‐i‐n+ diodes with the gold acceptor acting as recombination center. Theory and experimental results are in complete agreement for cn=3.2×10−8 cm3 s−1 and c−p=1×10−7 cm3 s−1. Finally, these values are compared with those given in the literature.

The temperature dependence of the capture cross section of negatively charged gold centers in n-type silicon for holes σ is determined in the temperature range of 55 K ≦ T ≦ 340 K from the temperature dependent breakdown voltage UBD of gold compensated pin diodes showing a negative differential resistance region. The temperature dependence of the capture cross section of neutral gold centers in the range of 193 K ≦ T ≦ 320 K, which was obtained in an earlier paper, is confirmed by means of small signal pulse measurements in the high injection regime of the same double injection diodes. The over-temperature caused by Joule heating in current filaments occurring in the high injection region of the stationary S-shaped I–U characteristic is measured for the first time using a large signal pulse method. Es wird die Temperaturabhangigkeit des Einfangquerschnitts von negativ geladenen Goldzentren in n-leitendem Si fur Locher, σ, im Temperaturbereich 55 K ≦ T ≦ 340 K aus der temperaturabhangigen Durchbruchsspannung UBD von goldkompensierten pin-Dioden, die einen Bereich negativen differentiellen Widerstandes aufweisen, bestimmt. Die Temperaturabhangigkeit des Einfangquerschnitts von neutralen Goldzentren im Bereich von 193 K ≦ T ≦ 320 K, die in einer fruheren Arbeit erhalten wurde, wird mittels einer Kleinsignal-Impulsmessung im Hochinjektionsregime von Doppelinjektionsdioden bestatigt. Die durch Joulsche Warme verursachte Ubertemperatur in Stromfaden, die im Hochinjektionsbereich der stationaren S-formigen I–U-Gharakteristiken auftreten, wird zum erstenmal mit einer Grossignal-Impulsmethode gemessen.

Investigations of current oscillations observed in high resistivity Au-compensated n+–i–in+ and p+–p+ silicon samples are reported. The specific resistivities of the i regions are 20 k Ω cm and about 105 Ωcm at the n-type Si and 14 k Ωcm at the p-type silicon, respectively. The dc I–U-characteristics and the contact preparation justify the assumption that single injection SCLC are attributable to the current oscillations and that double injection is negligible. The waveforms of the oscillations are not sinusoidal in general. The frequencies are in the range of 100 kHz at the 105 Ωcm material. In the 20 k Ω cm samples a pulse like waveform is typical for the current instabilities and the repetition rate of the pulses is about 10 kHz. Measurements using voltage pulses show that current oscillations are initiated a certain delay time after applying the voltage pulse, if a critical trap occupation is reached. Es wurden Stromoszillationen in hochohmigen Au-kompensierten n+–i–n+- und p+–i–p+-Siliziumproben untersucht. Die spezifischen Widerstande der i-Zone betrugen 20 k Ω cm und ca. 105 Ωcm bei dem n- und 14 k Ω cm bei dem p-Material. Die dc I–U-Kennlinien und die Kontaktherstellung lassen darauf schliesen, das der Ladungstransport durch Majoritatstragerinjection geschieht und das Doppelinjektion vernachlassigbar ist. Der zeitliche Verlauf des Stromes ist im allgemeinen nicht sinusformig. Die Wiederholfrequenzen liegen bei dem ca. 105 Ωcm-Material im 100 kHz-Bereich. Bei den 20 k Ω cm-Proben tritt ein impulsformiger Stromverlauf mit einer Wiederholfrequenz von ca. 10 kHz auf. Messungen mit Spannungsimpulsen zeigen, das die Oszillationen eine bestimmte Zeit zum Anschwingen benotigen und das eine kritische Trapbesetzung fur ihr Auftreten Voraussetzung ist.

Current oscillations were observed in Au-compensated Si samples with two Au Schottky contacts. The oscillations are not sinusoidal, their frequency is in the 100 kHz range. This is quite different from the observations of Holonyak et al. at p-i-n diodes, in which sinusoidal oscillations in the frequency range of 5 to 100 MHz were obtained. The occurrence of these oscillations can be explained by means of double injection if the injection model of Sze et al. is used. According to this model the minority carrier concentration strongly increases in a semiconductor provided with two Schottky contacts if the two depletion regions touch each other. The large ratio of the amplitude of the oscillations and the dc current, the deviation from the sinusoidal waveform, the low frequencies and the large range of bias in which these oscillations occur, however, justify the assumption that the current oscillations occur with single injection as well. An Au-kompensierten Silizium-Proben mit zwei Au-Schottkykontakten wurden Stromoszillationen beobachtet. Die Oszillationen sind im Gegensatz zu den von Holonyak et al. an p-i-n-Dioden gefundenen nicht sinusformig und liegen mit etwa 100 kHz weit unter der von Holonyak et al. angegebenen Frequenz von 5 bis 100 MHz. Das Auftreten der Oszillationen last sich mit dem Einsetzen der Doppelinjektion erklaren, wenn man dafur ein Modell von Sze et al. zugrunde legt. Danach steigt die Minoritatstragerkonzentration stark an, wenn sich die Sperrschichtweiten beruhren. Jedoch legen das beobachtete grose Verhaltnis der Oszillationsamplituden zu dem Gleichstrom, die Abweichung von der Sinusform, die niedrigen Frequenzen und der grose Spannungsbereich, in dem die Oszillationen auftreten, die Vermutung nahe, das die Stromoszillationen auch bei Einfachinjektion auftreten.

The low-temperature phonon specific heat of vanadium-based alloys V:Hf, V:Ta, and V:W has been studied theoretically on the basis of a Green's-function technique. A nearest-neighbor impurity model with radial and angular force-constant changes has been employed. The force-constant changes have been evaluated by fitting the measured lattice specific heat of these systems. The effect of volume change has been taken into account. The theory has been modified for comparatively higher concentrations of impurities. The resonances have been found in F/sub 1//sub u/-irreducible representations only. The local strength constants were found to be quite important in determining the increase or decrease of the transition temperature T/sub c/. It has been observed that T/sub c/ increases slightly if the force constants for a heavy impurity (Hf) change weakly, and T/sub c/ shifts to lower temperatures (V:Ta,W) if the changes are strong. The electron-phonon as well as electron-impurity interactions are discussed in detail. The calculated results for both properties are in good agreement with the experimental measurements.