Some of the basic requirements currently envisioned for advanced microelectronic devices and circuits are outlined and discussed in terms of fabrication techniques. Phenomenological aspects of laser processing of semiconductor materials are presented and related to the potential application of this technology for overcoming some of the fundamental limitations of conventional fabrication methods. Laser processing results obtained from a variety of siliconbased materials and test structures are presented and used to illustrate the unique features of the laser technique and the novel approach it brings to semiconductor device and circuit fabrication.

Visible-light illumination of accumulation layers on Zn0 surfaces produced by hydrogen-ion implantation at 80 K results in a substantial enhancement of the surface electron density, up to the enormous value of 6x1014 cm-2. The photoenhanced layer persists indefinitely after the light is switched off, and has an effective width of 10–20 A. On the basis of the results presented we tentatively suggest that in addition to the fully-ionized proton donors responsible for the initial implanted accumulation layer, H2+ ions are also introduced beneath the surface by the hydrogen implantation. Illumination dissociates these species and shifts the protons so produced into sites in which they become fully ionized, thus augmenting the surface electron density of the implanted surface.

High-resolution measurements reveal a double-peak structure in the oxygen KLL main line of ZnO which is absent in MgO. We suggest that part of this fine structure is due to contributions from interatomic transitions and, as such, corresponds to two maxima in the valence-band density of states of ZnO.

Strong hydrogen-implanted accumulation layers on ZnO surfaces, produced and maintained at 80 K, can be further enhanced by illumination with visible light. The attainable enhancement is surprisingly large, resulting in an enormous surface electron density of up to 6 × 1014cm−2, and persists indefinitely after the light is switched off. The photoenhanced layer is practically identical in width (10–20 Å) and transport characteristics to the implanted layer upon which it is based. Thus, it constitutes, just as the initial hydrogen-implanted layer, a two-dimensional electron accumulation layer, by far the strongest ever attained on any semiconductor surface. The photoenhancement effect is not fully understood. Various aspects of this effect are studied in an attempt to gain some insight into the processes involved. On the basis of the results presented we tentatively suggest that latent centers consisting of H+2 species are introduced by the hydrogen implantation, in addition to the fully ionized proton donors responsible for the implanted accumulation layer. Illumination dissociates these species and shifts the protons so produced into sites in which they become fully ionized, thus augmenting the surface electron density of the implanted surface.

The Auger spectra of the polar and prism surfaces of single-crystal ZnO were measured. The sensitivity factors derived from the differentiated spectra are 0.26 and 0.25 for a beam energy of 3 and 5 keV, respectively. These values agree fairly well with the theoretical calculations of Mroczkowski and Lichtman.

Low-energy hydrogen-ion implantation is use to produced extremely strong electron accumulation layers on ZnO. Such layers are 10–20 Å wide and resemble closely accumulation layers obtained by conventional methods. They are, however, completely insensitive to oxygen and thus constitute the only two-dimensional electron gas system on a surface that is both free and inert.

The penetration depths of protons in the (0001̄) face of ZnO produced by 100- and 400-eV hydrogen-ion bombardment are studied by three methods: calibrated argon-ion sputtering, calibrated etching, and space-charge capacitance measurements in the ZnO/electrolyte system. For the 100-eV implantation, the latter method provides unequivocal support to our previous conclusion that the protons, acting as fully ionized donors, penetrate only to a depth of 10–20 Å below the surface. The narrow space-charge layer so produced, having surface electron densities of up to 2 × 1014 cm−2, constitutes a quantized, two-dimensional electron gas system. In the 400-eV implanted surface, the proton penetration depth is considerably larger. In this case an approximate depth profile could be derived from the combined measurements. It consists of a Gaussian distribution, peaked about 40 Å below the surface with a standard deviation of some 80 Å. However, some 10% of the implanted protons are found to penetrate much deeper, being distributed up to 1000 Å or more below the surface. For 100-eV implanted surfaces, similarly large penetration depths were observed, but the percentage of the deep lying protons is less than 1%. Such huge penetration depths arise most probably from a channeling mechanism.

Studies are reported of ZnO surfaces prepared by a three-stage implantation procedure consisting of: (1) bombardment with a 100-eV hydrogen-ion beam of an insulating sample held at 200°C, a process that introduces a very high surface density of free electrons; (2) annealing at 300°C, which restores the initial insulating state of the surface, suggesting loss of all memory of the preceding implantation; and, finally, (3) re-bombardment with 100-eV ions, but now while the sample is kept at room temperature. The surfaces so produced are totally different from those reported previously in which only the last implantation stage had been applied. In addition to the narrow, electron-rich layer resembling very closely the accumulation-like layer observed on the latter surfaces, a second, much wider electron-rich layer also forms. The first layer, extending to about 20 Å below the surface proper, contains hydrogen donors which are fully ionized down to at least 10 K. The second layer is several thousand angstroms wide and the hydrogen donors in it are only partially ionized at room temperature, becoming completely unionized at 100 K. The enormous penetration range of the implanted hydrogen, as evidenced by the thickness of the wide layer, is very difficult to account for. Equally difficult to explain is the marked difference in the characteristics of the hydrogen donors in the narrow and wide layers. Some suggestions concerning these rather puzzling observations are put forward but at this stage they are largely of a speculative nature.

Implantation of 100-eV hydrogen ions on the (0001̄) face of ZnO produces extremely strong electron accumulation layers on the surface. Calibrated argon-ion sputtering measurements indicate that the implanted ions (consisting mostly of protons) penetrate to a depth of 10–20 Å beneath the surface. They act as fully ionized donors giving rise to a free electron layer of comparable depth and of surface electron densities up to 2×1014 cm−2. The narrow width, combined with detailed transport measurements, show that the implanted accumulation layers closely resemble ordinary accumulation layers on ZnO surfaces obtained, for example, by exposing the surface to atomic hydrogen. Thus the implanted layers, just as the ordinary accumulation layers, constitute a quantized, two-dimensional electron gas system. The important advantage of the implanted over the ordinary accumulation layers, however, is that they are completely inert to oxygen or even to room air. Annealing experiments provide estimates for the activation energies for release of the hydrogen ions from the surface layer. The results indicate the presence of several different types of lattice sites for the implanted ions.

Laser annealing techniques were successfully incorporated into standard MOS/SOS processing to increase transistor channel mobility and processing yield. Silicon islands were photolithographically defined and chemically etched (by KOH) on standard SOS wafers. The islands were exposed to radiation from an excimer laser (λ = 2490 Å) having a pulse duration of 25 ns, a beam size in the range of 0.1-0.2 cm2, and an energy density in the range of 0.5 - 1.0 J/cm2. Using standard processing techniques MOS transistors were fabricated and characterized. It was found that exposure at an energy density of ∼0.80 J/cm2results in rounding the Si island edges, thus eliminating the "V"-shaped groove profile of the gate oxide and improving Al step coverage. The electrical characteristics of MOS transistors fabricated over laser annealed islands exhibited a 30-percent increase in channel mobility with a small negative shift (<0.2 V) in the transistor threshold voltage.

Laser annealing techniques were successfully incorporated into standard metal-oxide-semiconductor silicon-on-sapphrie (MOS/SOS) processing to increase transistor channel mobility. Silicon islands were photolithographically defined and chemically etched (by KOH) on standard SOS wafers. The islands were exposed to radiation from an excimer laser (λ=2490 Å) having a pulse duration of 25 nsec, a beam size in the range 0.1–0.2 cm2, and an energy density in the range 0.5–1.0 J/cm2. Using standard processing techniques, MOS transistors were fabricated and characterized. It was found that MOS transistors fabricated over islands exposed to a beam having an energy density of 0.8 J/cm2 exhibit a 30% increase in channel mobility.

Laser annealing techniques were successfully incorporated into standard MOS processing to improve the quality of oxides grown over polycrystalline silicon (polysilicon). Polysilicon films (5000 Å thick) deposited over 1000 Å SiO2, grown over (100) bulk Si were exposed to a short pulse (20 nsec) of ruby laser radiation at an energy density of 1 J/cm2 and subsequently oxidized at 925 °C. The resulting oxides over the polysilicon were found to have leakage currents which are lower by over three orders of magnitude than oxides grown over polysilicon films which were not laser annealed. C-V measurements taken on the underlying polysilicon-SiO2-Si structure indicate that no deleterious effects were produced in the underlying structure by the laser radiation.

Laser annealing techniques were successfully incorporated into standard MOS processing to improve the quality of oxides grown over polysilicon. Polysilicon films (5000 Å thick) deposited over 1000-Å SiO2, grown over

Successful incorporation of laser annealing techniques into standard processing methods requires that the electrical characteristics of the devices not be degraded. In this work, a range of energy densities from pulsed u.v. and visible lasers which can be utilized in silicon on sapphire (SOS) technology to improve device performance without introducing any deleterious side effects is determined experimentally. Silicon islands were photolithographically defined and chemically etched (KOH) on standard SOS wafers which were subsequently exposed to pulsed (25 nsec) ruby (λ = 6943 Å) and excimer (λ = 2490 Å) laser radiation. Comparative studies of the effect of front and back side (through the sapphire) irradiation of the silicon on device performance were conducted. Using standard processing techniques, MOS transistors were fabricated after laser irradiation and electrically characterized. It was found that under certain conditions utilization of lasers in SOS processing, can result in an increase in the interface state density at both the top 〈100〉 Si-SiO2 interface and the bottom Al2O3-Si interface. However, a set of conditions exists, in which it is possible to apply laser annealing to standard SOS processing so as to increase MOS/SOS transistor channel mobility by over 30% without causing any degradation of the device electrical characteristics.

Thin (3000–5000Å) low pressure chemically vapor deposited (LPCVD) films of polycrystalline silicon suitable for microelectronics applications have been deposited from silane at 600°C and at a pressure of 0.25 Torr. The films were phosphorus implanted at 150 KeV and electrically characterized with the annealing conditions and film thickness as parameters, over a resistivity range of four orders of magnitude (103–107Ω/□). Annealing during silox deposition was found to result in a lower film resistivity than annealing done in nitrogen atmosphere. Resistivity measurements as a function of temperature indicate that the electrical activation energy is a linear function of 1N(N is the doping concentration), changing from 0.056 eV for a doping concentration of 8.9 × 1018 cm−3 to 0.310 eV for doping concentration of 3.3 × 1018 cm−3. The grain boundary trap density was found to have a logarithmically decreasing dependence on the polysilicon thickness, decreasing from 1.3 × 1013 cm−2 for 2850Å polysilicon film to 8.3 × 1012 cm−2 for 4500Å polysilicon film.

varied from 0.2 J . cm-2 to 0.8 J . cm-'. No dielectric encapsulating layers were deposited on the InP surface prior to electron pulsing. Threshold pulse energies have been established for obtainin electrical activity and sheet carrier concentrations -3 X lo1 cm-* which compare favorably with thermal annealing have been achieved. Profiling through layer stripping and differential Hall measurements indicate that although conduction occurs mainly at depths found in thermally annealed layers, an anamolous surface component is also present. The mobilities -600 cmz . V-' s-' are only about half of the thermally annealed values. No carrier freezeout occurs at 78 K as has been reported in one study on laser annealed InP' and so the conduction does not appear to be dominated by a defect deeper than the shallow dopant level. While the annealed surfaces appear to retain their initial polish with some pitting, interference contrast microscopy reveals a very fine regrowth ripple extending over the surfaces. Small isolated craters, indicating localized heating, account for the pitting. These, as well as the regrowth pattern, become more pronounced as the pulse energy increases and particularly beyond the threshold for electrical activation. f

The procedure of preparing starting materials of HgI2 pre-treated with iodine and crystal growth from the vapor phase using the temperature oscillation method, TOM, in both a horizontal and vertical furnace is reviewed. The nuclear radiation detector properties of two of the best representative crystals grown in a horizontal furnace from iodized material and in a vertical furnace from non-iodized material are shown and discussed. The smallest full width half-maximum, fwhm, so far detected with a 10×8×0.5 mm3 mercuric iodide detector is 4.5 keV for the 662 keV photopeak of 137Cs.