Thick Silicon Substrate Research Articles

Low-Temperature Infrared Absorption Measurement For Oxygen Concentration and Precipitates In Heavily-Doped Silicon Wafers

AbstractWe present a new IR absorption technique of measuring the dissolved interstitial oxygen concentration [Oi] and its reduction Δ [Oi] due to oxygen precipitation of the heavily-doped silicon crystal with doping level of about 1019 atoms/cm3. The method consists of the three steps: bonding the silicon wafer to a thick FZ silicon substrate by heat-treatment, thinning the wafer, and measuring the height of the 1136-cm−1 absorption peak of Oi at a temperature below 5 K. For a heavily doped wafer and the heavily doped substrate of an epitaxial wafer, we demonstrate examples of measuring the initial [Oi] and Δ [Oi] due to heat-treatment. Using this method, we investigate oxygen precipitation characteristics of the wafer heavily doped with boron. We found that the enhanced oxygen precipitation due to heavy boron-doping is expected if we perform preanneal at temperatures below 700°C.

Transmission characteristics of a supermirror bender

A multichannel micro-bender has been developed using Ni/Ti supermirrors coated on both sides of 0.3 mm thick silicon substrates. The bender has a characteristic wavelength of 5.0 Å. The radius of curvature is 1660 mm, the total length is 48.4 mm, and the beam size is 12 mm × 55 mm. Performance tests on the neutron transmission have been made using facilities at the JRR-3M reactor. The measured characteristic wavelength agreed with the design value. A deflection of 1.6° has been obtained, and transmission of 76% was observed with neutrons of 12.6 Å.

Silicon-gap Fabry–Perot filter for far-infrared wavelengths

We developed a far-infrared Fabry-Perot filter constructed from a single silicon substrate. The limiting resolving power caused by beam divergence of a silicon-gap Fabry-Perot filter is approximately 10 times higher than that of a vacuum-gap Fabry-Perot filter because of the large index of refraction of silicon. The filter thus permits compact, high-throughput optical systems. Metal mesh patterns microlithographed on each face provide enhanced, wavelength-dependent face reflectivity. We tested the performance of filters with metal mesh patterns consisting of inductive crosses and capacitive squares. A Fabry-Perot filter developed for a rocketborne astrophysics experiment with a capacitive square metal mesh pattern achieves a resolving power of λ/Δλ(FWHM) =160 at λ= 158 µm, with a peak transmittance of 37% over an active aperture of 6.9 mm for an ƒ/3.8 optical beam at 15° incidence. The absorptivity of a 240-µm thick silicon substrate patterned with capacitive metal mesh is A ≲ 1% per pass, including loss in both the silicon and the metal mesh.

Constrained-film sintering of a gold circuit paste

We studied the constrained-film sintering of a gold circuit paste used in microelectronic packaging applications. Optical techniques were developed to determine the shrinkage profiles of constrained and free films and stresses generated during sintering in the constrained films. Constrained films approximately 60 μm thick were made by multiple screen-printing of the gold paste on rigid alumina substrates, while the free films were obtained by peeling off portions of the gold films from the substrate after binder burnout. Constrained films for stress measurement were made by multiple screen-printing on an oxidized 25 μm thick silicon substrate. Sintering runs were done in a hot stage at temperatures between 650 °C and 900 °C. The densification rates were much lower in the constrained films than those in the free films. The in-plane tensile stresses in the constrained films, determined by wafer curvature measurement, rose rapidly to a maximum level of 510 kPa during the initial stage of sintering and then gradually decreased. The reduction in the sintering potential due to the hydrostatic stress is not large enough to completely account for the retarded densification in constrained films. SEM micrographs of the film microstructures after sintering showed no-significant difference in grain growth kinetics between the constrained and free films. However, the activation energy for densification was found to be very different between the two types of films, 90.1 ± 4.3 kJ/mole for the free film and 188.8 ± 6.7 kJ/mole for the constrained film. We suggest that the retarded densification kinetics in the constrained gold films is due to (i) the reduction in the sintering potential by the hydrostatic stress and (ii) a change in the dominant sintering mechanism from grain-boundary diffusion in the free films to lattice diffusion in the constrained films.

Performance of a bender for a water cooled monochromator crystal at a high power wiggler beamline of the ESRF

A bender has been developed for a directly water cooled monochromator crystal. The performance was tested at the materials science wiggler beamline (BL2) of the European Synchrotron Radiation Facility. The x rays were reflected by a 0.6 mm thick silicon wafer bonded to a 40 mm thick silicon substrate with grooved cooling channels at the surface. These channels are 0.5 mm wide and 2 mm deep with 1 mm fins in between. The input power on the monochromator crystal was measured using a calorimeter. At an input power of 1440 W the rocking curve width of the Si (111) reflection at 13 keV could be decreased by using the bender mechanism from 17 to 9.5 arcsec. The remaining broadening compared to the low power rocking curve was about 1.5 arcsec and was due to residual bonding or bending strain. Result of finite elements analysis is also shown.

Heterodyn interferometer for the detection of electric and thermal signals in integrated circuits through the substrate

Abstract A laser diode based probing system for the interferometric detection of charge density and temperature modulations accompanying electric signals in integrated circuits has been developed. Its main advantage compared to previously introduced measuring schemes is a versatile and inexpensive positioning system for the probing and reference laser beams, noise reduction due to the use of heterodyn techniques and the absence of polarizing elements. The temporal resolution is limited by the laser diode pulse width to 500ps. The probe and reference beam are both focussed to a diameter of 1.5μm through a 400μm thick silicon substrate which determines the spatial resolution. The system's abilities are demonstrated in measurements of bipolar and CMOS test structures.

Properties of Piezoelectric Pzt Thin Films for Microactuator Applications

AbstractThe piezoelectric properties of lead zirconate titanate (PZT) thin films deposited on thick silicon substrates and thin silicon membranes were investigated using optical interferometry. The effect of the geometrical constraints and clamping effects on the piezoelectric response is discussed. The study of the dielectric permittivity and the loss as a function of the amplitude of the alternating electric field reveals that extrinsic contributions to the dielectric permittivity become active at large fields. The DC electric field has the effect of freezing out the extrinsic contributions. The influence of the dielectric loss on the piezoelectric properties is discussed.

Experimental studies on primary and secondary pyroelectric effects in Pb(ZrxTi1−x)O3, PbTiO3, and ZnO thin films

The pyroelectric coefficients and pyroelectric response in lead zirconate titanate (Pb(ZrxTi1−x)O3), lead titanate (PbTiO3), and zinc oxide (ZnO) thin films (0.1–2.0-μm thick) have been studied for possible integrated thermosensor applications. Pyroelectric properties of these films deposited on thick (500-μm) silicon substrates and thin (1.0-μm) polysilicon membranes have been investigated. The measured pyroelectric coefficients for these materials are 70, 95, and 1.0 nC/cm2 K for Pb(Zr0.54Ti0.46)O3, PbTiO3, and ZnO, respectively. Coupling effects between the pyroelectric film and substrate were studied. It was observed that the primary pyroelectric effect dominates the pyroelectric response in Pb(Zr0.54Ti0.46)O3 and PbTiO3 thin films while the secondary effect is dominant in ZnO thin films.

Sensitivity and selectivity of intraneural stimulation using a silicon electrode array

Artificial electrical stimulation of peripheral nerves needs the development of multielectrode devices which stimulate individual fibers or small groups in a selective and sensitive way. To this end, a multielectrode array in silicon technology has been developed, as well as experimental paradigms and model calculations for sensitivity and selectivity measures. The array consists of twelve platinum electrode sites (10 x 50 microns at 50 microns interdistance) on a 45 microns thick tip-shaped silicon substrate and a Si3N4 insulating glass cover layer. The tip is inserted in the peroneal nerve of the rat during acute experiments to stimulate alpha motor fibers of the extensor digitorum longus muscle. Sensitivity calculations and experiments show a cubic dependence of the number of stimulated motor units on current amplitude of the stimulatory pulse (recruitment curves), starting at single motor level. Selectivity was tested by a method based on the refractory properties of neurons. At the lowest stimulus levels (for one motor unit) selectivity is maximal when two electrodes are separated by 200-250 microns, which was estimated also on theoretical grounds. The study provides clues for future designs of two- and three-dimensional devices.

Integrated pyroelectric detector arrays with the sensor material PVDF

Abstract Integrated PVDF pyroelectric radiation detectors have been made, using a simple technique to interface the pyroelectric material with the silicon substrate. The silicon substrates incorporate the electronics for a 8x1 array and a 2x2 array. The relevant sensor parameters voltage responsivity, detectivity and the thermal crosstalk are measured within a frequency range from 0.01 Hz to 5000 Hz. With the 400 μm thick silicon substrate the voltage responsivity is typically 100 V/W, the maximum detectivity is 7×106 cm□Hz/W at a frequency of 30 Hz. An improvement of both voltage responsivity and detectivity is possible by reducing the heat loss to the silicon substrate. This can be realized by a reduction of the substrate thickness, at least underneath the detector area. A further improvement is possible by a reduction of the capacity of the electronic circuit on the silicon chip and by the use of ferroelectric materials with higher pyroelectric coefficients, for example TGS.

Fabrication of 25nm wide gold lines using nanometer scale lithography and ionized cluster beam deposition

Abstract It becomes increasingly difficult to make continuous metal lines with well defined thickness and edges by the lift-off technique as the line width is decreased. We describe in this paper a technique in which the combination of high resolution electron beam lithography and ionized cluster beam (ICB) deposition has enabled very high quality gold lines (≌25nm wide) to be obtained on thick single crystal silicon substrates.

Monte Carlo simulation of the energy dissipation profiles of 30, 50 and 100 keV incident beams in a layered structure in electron beam lithography

This paper presents a Monte Carlo simulation of the energy dissipation profiles of 30, 50 and 100 keV incident beams in thin film (0.4μm) of electron resist, polymethyl methacrylate (PMMA), on thick silicon substrate in electron beam lithography. The radial scattering and the energy loss of incident electrons (including backscattered electrons from the substrate) are simulated under the illumination of ideal point source and Gaussian round beam spot source, and the histories of 30000–50000 electrons are computed.

Investigation of crystallographic properties of thin germanium crystals grown on silicon substrates by chemical vapor deposition

The quality of germanium crystals deposited from the gas phase by chemical vapor deposition using pyrolytic decomposition of GeH 4 in a helium atmosphere at various growth temperatures on silicon substrates was determined. X-ray diffraction and rocking curve measurements proved to be very useful in determining the degree of preferred orientation of the germanium deposit, since they distinguish clearly between the reflections of the thin germanium deposited layer and those of the thick silicon substrate. Therefore they permit fairly accurate calculations. Laue measurements, in this case, proved to be unsatisfactory because of inadequately low resolution. The results show that a preferred orientation of germanium crystallites in the layer of up to 99.9% was reached.

Planar multijunction high voltage solar cell chip

Integrated circuit technology has been successfully developed to design and fabricate a new type of small area planar multijunction high voltage solar cell chip for concentrated sunlight applications. Each of these 1×1 cm solar cell chips was a monolithic device consisting of six internally series interconnected unit cells, fabricated on 75 μm thick p-type single crystal silicon substrate. Each chip consisted of 1.42×9.63 mm n+/p collecting junctions on the back of the wafer. The illuminated front surface area was divided into 0.3 μm deep n+ regions which form front surface field regions corresponding to the n+/p unit cells positioned beneath. A five photomask level photolithographic process together with a standard microelectronics batch process technique was employed to construct the PMJ solar cell chip. The open circuit voltage of the solar cell chip increased rapidly with illumination up to about 4 AMl suns, and then began to saturate at the sum of the individual unit cell voltages of 3.5 V above 4 AMl suns. A short circuit current density per unit cell of 300 mA/cm2 at 20 AMl suns was observed. This low value is attributed to a low minority carrier diffusion length in the base region of the solar cell chip. The suggested process modifications should significantly increase the device efficiency.

Multilevel resist for lithography below 100 nm

Features as small as 25 nm have been made with electron-beam lithography using multilevel resists on thick silicon substrates. Liftoff patterning of metal lines and reactive ion etching of silicon have demonstrated the possibility of making device structures with lateral dimensions below 100 nm.

50−nm silicon structures fabricated with trilevel electron beam resist and reactive-ion etching

A trilevel electron beam resist has been used to make 25-nm metal features on thick silicon substrates. Using this metal as a mask for reactive ion etching, silicon structures 0.33 μm deep have been fabricated. The resist consists of a thin upper layer of polymethylmethacrylate (PMMA), a middle layer of Ge, and a lower layer of co-polymer of methylmethacrylate and methacrylic acid, P(MMA/MAA). High-resolution patterns are written in the upper resist layer and are transferred to the lower layers by reactive-ion etching. Completed resist stencils have 300-nm high walls with near-vertical profiles and are suitable for liftoff processing.

Sensitivity of ion induced X-ray analysis for surface layers on thick silicon substrates

Surface contaminations on silicon slices and contaminations in surface layers deposited on thick silicon substrates were investigated by means of ion induced X-ray analysis. Sensitivity limits of foreign atoms are given for proton and nitrogen impact in dependence of projectile energies. They were derived using calculated K-shell ionization cross-sections as well as measured X-ray and γ-ray background spectra. The validity of the model used for characteristic cross-section calculations was proved by comparing the theoretical with experimental results. Some examples are given for the analysis of the basic material for the production of semiconductor electronic devices.