The etch conditions affecting the etching of the fluorinated polyimide films in RF plasma using oxygen or fluorine-containing oxygen has been investigated. The effect of power, oxygen gas flow rate, and gas composition on the etch rate of fluorinated polyimide have been determined. The etch rate of the fluorinated polyimide increases linearly with the power and oxygen gas flow. The saturation at high oxygen flow rate indicates a saturation or steady state achieved at the polyimide-oxygen reaction interface. However, the etch rate increases when CF4 is added to oxygen, up to about 10% CF4 in O2, and then decreases to a smaller and CF4 concentration independent value. The etch selectivity of hard mask against fluorinated polyimide has been determined. The PECVD silicon nitride and PETEOS are found to be excellent hard mask for pattering these polyimides. The trench profile of the polyimide film also has been examined by patterning and etching the different trench sizes in fluorinated polyimide. It is concluded that this fluorinated polyimide can be etched with oxygen or fluorine containing oxygen plasma.

ULSI Interconnects require insulative materials with as low a dielectric constant as possible in order to minimize crosstalk and parasitic capacitance. Transmission line simulations indicate that crosstalk in parallel interconnect lines can be dramatically reduced by lowering the dielectric constant of the insulation from 4 to 2. Polytetrafluoroethylene (PTFE) has a desirably low dielectric constant (2.05), but has previously been difficult to deposit in thin films suitable for integrated circuit applications. PTFE has other desirable properties, including temperature resistance in excess of 400 C and outstanding chemical resistance.

A novel liquid material has been developed which permits the spin coat deposition of full density PTFE films from 0.2 to 1.0 microns thick. The deposition liquid is a solvent-free, stable PTFE nanoemulsion consisting of fully cured < 0.05 micron particles, surfactant, and water. The nanoemulsion is an equilibrium phase which is thermodynamically stable, optically clear, and has low viscosity. These properties are achieved because of the unusually small particle size of the nanoemulsion. The films are uniform in thickness with a standard deviation of < 2% and edge-to-center variation of < 5%. The films have a weight loss rate of less than 0.008%/min at 425 ° C. Good adhesion to Al, Si3N4, Si, and SiO2 is obtained when the films are evaluated per ASTM D3359-93. Several reseachers have reported methods by which various materials may be deposited onto PTFE with acceptable results.

This study characterizes low pressure chemically vapor deposited B-N-C-H as a low dielectric constant material for interlevel dielectric applications. These films are synthesized over a temperature range of 400 to 600 °C and various flow rate ratios using triethylamine borane complex (TEAB) and NH3 as precursors. The dielectric constant of these films exhibit values which varied in the range of 2.6 to 3.5 depending on processing conditions. Low dielectric constant values are achieved at film compositions which approached stoichiometry and have minimal carbon content. The variations in the structural, optical, mechanical, and chemical properties of these films as a function of deposition conditions are also discussed.

The phenomenon of Ti-interlayer mediated epitaxy (TIME) of CoSi2 on Si(100) has attracted much academic and technological interest. As yet, the role of the interlayer, Ti, is not fully understood. The various drawbacks of the TIME process have driven the search for a better interlayer. New results are presented which demonstrate the efficacy of a thin SiOx layer, grown in a peroxide-containing aqueous solution, in inducing nearly perfect epitaxial growth of CoSi2 on practically all surfaces of Si. This technique, dubbed oxide mediated epitaxy (OME), allows a thin layer of epitaxial CoSi2 to grow sub-surface, leaving the SiOx layer largely on the surface of the silicide. An interesting result of the surface oxide cap is a significant re-evaporation of cobalt observed during deposition at elevated temperatures. Thicker (10-30nm), excellent quality, CoSi2 single crystal thin films have been grown by repeated growth sequences on Si(100), (110), (211) and (511). Nearly perfect type A oriented CoSi2 layers were grown on Si(111) using mixed A/B oriented template layers.

Ultra-Shallow p+/n and n+/p junctions were fabricated using a Silicide-As-Diffusion-Source (SADS) process and a low thermal budget (800÷900 °C). A thin layer (50 nm) of CoSi2 was implanted with As and BF2 and subsequently diffused at different temperatures and times to form two Ultra-Shallow junctions with a junction depth of 14 and 20 nm. These diodes were extensively investigated by I-V and C-V measurements in the range of temperature between 80 and 500 K. TEM delineation was used to controll the junction uniformity.

The effects of size and shape of lateral confinement on the formation of NiSi2, CoSi2 and TiSi2 on silicon inside miniature size oxide openings have been investigated. Epitaxial growth of NiSi2 of single orientation on (111)Si was found to occur at a temperature as low as 400 °C inside both contact holes and linear openings of 0.3 μm or smaller in size. Contact holes were found to be more effective in inducing the epitaxial growth of NiSi2 of single orientation than that of linear openings of the same size. The effects of size and shape of lateral confinement on the epitaxial growth of NiSi2 on (111)Si are correlated with the stress level inside oxide openings. The faceting of CoSi2 was found to occur at a lower temperature inside oxide openings of smaller size. C49-C54 TiSi2 transformation was observed to be more difficult on both blank and BF2+ implanted (001)Si inside smaller size oxide openings.

We studied the kinetics of the high resistivity to low resistivity phase transformation for Ti and Co silicides on deep-sub-micron geometries. Fundamental differences between the growth characteristics for Co and Ti result in different scaling behavior. While the the TiSi2 C54 phase grows by a random nucleation and growth process from the polymorphic TiSi2 C49 phase, CoSi 2 grows by a diffusion limited process from CoSi. A strong linewidth and C49 grain size dependence for the TiSi2 C49 to C54 transformation can be related to low nucleation density. A Johnson-Mehl-Avrami analysis was performed for the TiSi2 C49 to C54 transformation obtaining the distribution of Avrami exponents and transformation times for individual 0.26 μm lines, showing that all lines transformed with similar one-dimensional growth characteristics. We found a strong dependence of the half-transformation times on film thickness and linewidth. While activation energies depend strongly on film thickness, ranging from 4.2 to 5 eV for films 64 to 28 nm thick, they are insensitive to linewidth indicating a different nature for the effect of linewidth and thickness. We also found a reduction of agglomeration temperatures with decreasing linewidth or film thickness resulting on a narrower process window for deep-submicron devices. A small linewidth dependence was measured for CoSi to CoSi2 transformation rates, with activation energies of 2 to 2.2 eV for 0.27 μm and wider lines. Both Co and Ti selfaligned silicide processes were implemented successfully into a 0.18 μm technology.

The formation of TiSi2 from deposited Ti layers on Si and the subsequent transformation of TiSi 2 from the C49 to the C54 phase have long been of concern, particular for the silicide formation on heavily doped, narrow polycrystalline Si lines. In this work, phase formation during rapid thermal annealing of Ti/Mo bilayers sequentially deposited on blanket Si wafers and on narrow polycrystalline Si lines (0.6 μm width) is studied. The Mo layer is always 0.5 nm thick, and the Ti either 45 nm or 60 nm. It is shown that the initial physical separation of Ti from Si by the interposed Mo layer leads to complete prevention of the formation of the C49 phase. Instead, a Mo-bearing silicide phase of hexagonal structure forms first, and the C54 phase nucleates and then grows on top of it via Si diffusion through the growing silicide layers. The significance of this finding is that the usual sequence for the formation of TiSi2,. e. the C49 phase forms as a result of the Ti-Si interaction and the C54 phase forms as the product of phase transformation, is altered by the interposition of a thin refractory metal layer, here Mo. The difficulties involved in nucleation and growth of the C54 phase are then overcome, yet by a different approach than the usually employed ones which rely on ion implantation to enhance the formation of the C49 phase and the subsequent transformation to the C54 phase.

A new Ti salicide technology that uses nitrogen diffusion from a TiN cap layer by RTA in an argon ambient is demonstrated. The key point for achieving a fine-line Ti salicide iscontrolling the two competing reaction processes in thin Ti (<30 nm): nitridation at the Ti surface, and silicidation at the interface between Ti and Si. In the conventional Ti silicidation process using atmospheric nitrogen RTA, however, control of nitridation is difficult due to a high concentration of nitrogen at the Ti surface. Therefore, the remaining TiSi2 film is very thin and contains larger amount of nitrogen [1]. The new technology provides good controllability of Ti nitridation for thin Ti by using an argon atmospheric RTA.

A major advantage of nitrogen diffusion from a TiN cap layer is controllability of the nitrogen concentration at the interface between TiN and Ti. After TiN and Ti sputtering, silicidation was performed by two-step annealing in argon (RTA1: 680°C, 30 s; RTA2: 800°C, 10 s). When the thickness ratio (TiN/Ti) was 1, Ti2N formed on the field oxide. The Ti2N layer suppresses excessive silicidation over the field oxide in the same way that TiN does. Sheet resistance results show that silicidation is suppressed by the impurity effect in the case of thinner Ti (<20 nm). Furthermore, when TiN is thick (>20 nm), large metal strength retards silicidation [2]. Optimization of TiN/Ti thickness (20/20 nm) is essential for achieving low sheet resistance of 10 Ω for p+ and n+ quarter micron lines.

Scaling of MOSFETs into the deep submicron regime requires novel metallization schemes to form low resistivity contacts on ultra-shallow junctions. In this paper, we present our recent results on rapid thermal chemical vapor formation (RTCVF) of TiSi2. In this process, the gaseous Ti source, TiCl4 (g), reacts with solid Si to form C54 TiSi2(s) at temperatures as low as 700°C with a resistivity of 15-20μΩ-cm without a follow-up anneal. In this paper, we explore the previously reported barrier for nucleation of TiSi2 on Si at temperatures below 800°C. Without proper surface preparation, this barrier results in an incubation time which can vary according to the conditions of the surface and the deposition environment. We show that contrary to general belief, surface morphology instead of surface cleanliness is the most likely contributor to this barrier. We also show that if in-situ deposition of a Si-Ge layer precedes TiSi2 formation, the incubation time can be completely eliminated. Experiments performed in a temperature range of 650°C - 800°C indicate an approximate activation energy of 100 kJ/mol. The process provides excellent selectivity to both SiO2 and Si3N4 and little growth rate dependence on patterns in the 2 μm - 200 μm regime.

Shallow contact metallization of SiGeC was studied in anticipation of this alloys use in low power applications. It has been shown that in the solid state reaction of Co on (100) Si, that Co is the moving species with proper annealing conditions. This prevents the formation of Kirkendal voiding in certain device structures. This work studies the Co and Ti metallization of SiGeC. A bilayer of 44 nm of Co on 7 nm of Ti, were electron beam evaporated onto epitaxially grown Si0.77Ge0.21C0.02. The samples were rapid thermal processed at 600 and 900 °C for up to two minutes in a nitrogen ambient. The analysis techniques used were Rutherford backscattering spectrometry which included the used of the 4.27 MeV 12C(α,α) 12C resonance reaction, glancing angle x-ray diffraction, During annealing at all temperatures, Co diffused through the Ti layer and formed CoSi. This phase was confirmed by x-ray diffraction. The Co displaced the Ti to the surface. At 600 °C, Ge diffused to the surface layer, while at 900 °C it was rejected back into the original SiGeC. The sample annealed at 600 °C was subsequently annealed at 900 °C. The Ge in the surface layer was rejected from the surface layer, diffused across the CoSi and back into the SiGeC.

Thin gadolinium silicide layers have been formed by channeled ion beam synthesis. Continuous and heteroepitaxial GdSil.7 layers with a hexagonal structure and a χmin value of 10% are prepared by Gd ion implantation at 90 keV to a dose of 1.3x1017/cm2 at 450°C in Si(111) using channeled implantation. The hexagonal phase of GdSi1.7 is stable up to a temperature of 850°C. Both the crystalline quality and the phase stability are much better than the results obtained by conventional techniques. Annealing at > 900°C suddenly changes the χmin value of the silicide layer from 10% to 100%. X-ray diffraction shows that the phase has changed to orthorhombic. RBS/channeling, x-ray diffraction and transmission electron microscopy are used in this study.

In view of their potential application in ULSI technology, nickel silicide films were formed on undoped and doped Si(100) substrates. Nickel films of varying thicknesses were sputter-deposited onto the substrates and silicidation was performed ex-situ by rapid thermal annealing in nitrogen ambient. The electrical sheet resistance of the silicides was studied as a function of film thickness and annealing temperature. The process window for forming the NiSi phase and the thermal stability of the NiSi phase were determined as a function of film thickness.

Epitaxial growth of NiSi2 on (111)Si inside 0.1-0.6 4m in size oxide openings prepared by electron beam lithography has been studied by field emission scanning electron microscopy, transmission electron microscopy and thin film stress measurement. Striking effects of size and shape of deep submicron oxide openings on the growth of NiSi2 epitaxy were observed. Epitaxial growth of NiSi2 of single orientation on (111)Si was found to occur at a temperature as low as 400 °C inside both contact holes and linear openings of 0.3. μm or smaller in size. Contact holes were found to be more effective in inducing the epitaxial growth of NiSi2 of single orientation than that of linear openings of the same size. The effects of size and shape of lateral confinement on the epitaxial growth of NiSi2 on (111)Si are correlated with the stress level inside oxide openings.

Two different Si(100) substrates, the 4°off-axis and the on-axis Si(100), were prepared. Ti thin films were deposited in an e-beam evaporation system and the amorphous layers of Ti-silicide were formed at different annealing temperatures. The Si(100) substrates before Ti film deposition were examined with AFM to verify the atomic scale roughness of the initial Si substrates. The amorphous layer was observed by HRTEM and TEM. And the chemical analysis and phase identification were examined by AES and XRD. The Si(100) substrate after HF clean shows the atomic scale microroughness such as atomic steps and pits on the Si surface. The on-axis Si(100) substrate exhibits much rougher surface morphologies than those of the off-axis Si(100). These differences of atomic scale roughnesses of Si substrates result in the difference of the thicknesses of amorphous Ti-silicide layers. The amorphous layer thicknesses on the on-axis exhibit thicker than those of the off-axis Si(100) and these differences inamorphous layer thicknesses became decreased as annealing temperatures increased. These indicate that the role of the atomic scale roughness on the amorphous layer thickness is much significant at low temperatures. In this study, the correlation between the atomic scale roughness and the amorphous layer thickness is discussed in terms of the atomic steps and pits based on the observation with using analysis tools such as AFM, TEM and HRTEM.

Changes in current transport and barrier heights of Ni-Si contacts as it undergoes atomic rearrangement and redistribution of charges under transient light annealing is studied with time resolution of 0.6 msec. Formation of an intermixed Ni-Si disordered layer by Ni-diffusion is shown by Auger data. Intrinsic barrier height of 0.7 eV increases to 0.82 eV as the spatial extent, disorder and density of Ni atoms which introduce new localized ststes at Ev+0.7 eV increases. Electronic properties of silicide contacts are affected by local interfacial bonds than by the characteristic of later grown silicide.

The Partially ionized beam (PIB) deposition technique was used to deposit CoGe2 thin films heteroepitaxially on GaAs(100) substrates in a conventional vacuum. For the CoGe2(001)/GaAs(100) system, which leads to an Ohmic contact, a substrate temperature of 280°C and ∼1200 eV Ge+ ions are required. Reducing the ion energy or lowering the substrate temperature both produce a different orientation in the films. Films deposited at 280°C with a zero accelerating potential for the ions, and those deposited at 200°C with -1200 eV Ge+ ions result in a CoGe2(100)//GaAs(100) type orientation domination, leading to rectifying behavior.

Interfacial microstructure and elemental diffusion of Pd/Ge/Ti/Au ohmic contact to n-type GaAs have been investigated using x-ray diffraction(XRD), Auger electron spectroscopy(AES), and cross-sectional transmission electron microscopy(XTEM), and their results are used to interpret the electrical properties. The lowest contact resistance of 0.43 Ωmm is obtained after annealing at 380°C. The contact is thermally stable even after isothermal annealing for 5h at 400°C. The good Pd/Ge/Ti/Au ohmic contact is due to the formation of both AuGa and TiO compounds. The AuGa compound enhances the creation of more Ga vacancies, followed by incorporation of Ge into Ga vacancies and TiO compound suppresses As outdiffusion from GaAs substrate, respectively.

InP/In0.53Ga0.47As heterojunction bipolar transistors with high current gain for optoelectronic applications place stringent requirements on the ohmic contact to the base layer of moderately doped (p < 1×1019 cm−3) In0.53Ga0.47As. Contact resistivity should be <l×10−6 Ωcm2 and low depth of penetration is necessary considering the small base thickness of approximately 100 nm. The authors have recently presented data on Pd/Zn/Au/LaB6/Au contacts on p-In0.53Ga0.47As (doped to 4×1018 cm−3) with low contact resistivities of l×10−6 Ωcm2. In this paper, details are given on the optimization of the contact composition and annealing conditions of the metallization that resulted in shallow and low-resistive contacts. Alternatively, it is shown that Au-free Pd/Zn/Sb/Pd contacts on p-In0.53Ga0.47As have exhibited even lower resistivities, i.e. 3-6×10−7 Ωcm2. Backside SIMS measurements revealed a depth of penetration as low as 20 nm for this contact scheme. Aging tests at temperatures of 300 - 400 °C have demonstrated that the electrical characteristics of both types of metallization were sufficiently stable to withstand the typical processing steps for device passivation.

An Ohmic contact system comprising of Pd/Sn metallization has been developed for n-GaAs and compared with Pd/Sn/Au metallization. Surface morphology of the contacts is investigated using surface profilometry measurements and Scanning Electron Microscopy (SEM). The contact depth profiles are analyzed by Secondary Ion Mass Spectrometry (SIMS). Contact resistivities, Pc, of the proposed metallizations are measured using a conventional Transmission Line Model (TLM) method. A lowest ρc, of ∼2.07×10−5 Ω-cm2 was obtained with a Pd(50 nm)/Sn(125 nm) contact on 2×1018 cm−3 n-GaAs after annealing at 400 °C for 30 min. A Au overlayer improves the characteristics of the Pd/Sn contacts. The Pd(50 nm)/Sn(125 nm)/Au(100 nm) contact shows a lowest ρc of ∼1.29×10−6 Ω-cm2 after annealing at 330 °C for 30 min. The Pd/Sn/Au contacts exhibit superior properties compared to those of alloyed five-layer Au/Ge/Au/Ni/Au contacts.