Mao‐Chieh Chen

Thermal stability of cobalt silicide thin films on Si(100)

The thermal stability of blank and BF2−‐implanted cobalt silicide (CoSi2) films annealed in a furnace with flowing nitrogen was investigated. It was found that BF2+ implantation can significantly stabilize thin silicide films during high‐temperature annealing. This result can be attributed to an increase in surface and interface energy. For a CoSi2 film with a thickness of 350 A, the silicide releases its high surface energy through low‐energy silicon surface exposure at elevated annealing temperatures (≥800u2009°C). The optimal BF2+ implantation energy for a cobalt silicide layer 350 A thick is 50 keV. At this energy, a dose of 2×1015 cm−2 is sufficient to improve the high‐temperature stability of CoSi2 film. The highest annealing temperature without degrading the CoSi2 film can be increased by 100u2009°C using the optimal implantation conditions.

Electrical and microstructural characteristics of Ti contacts on (001)Si

An investigation of the electrical and microstructural characteristics of the Ti contact on silicon has been carried out. The presence of As in Ti/n+-Si samples was found to retard the formation of polycrystalline silicide (p-silicide) compared with that in Ti/p+-Si samples with BF2+ implantation. Amorphous interlayers (a-interlayers) were found to be present in both Ti/n-Si and Ti/p-Si samples annealed at temperatures of and lower than 450u2009°C. Although the Schottky barrier heights (SBH’s) vary for about 0.05–0.08 eV for samples annealed over a temperature range from room temperature to 900u2009°C, SBH’s at the a-interlayer/n-Si and a-interlayer/p-Si were measured to be about 0.52–0.54 and 0.59–0.57 eV, respectively. The specific contact resistance (ρc) in the Ti/n+-Si system was measured to be the lowest with a value of 1.4×10−7 Ωu2009cm2 when the a interlayer is present. In Ti/p+-Si system, the minimum ρc is about 3×10−7 Ωu2009cm2. The variation in contact resistance with annealing temperature for both Ti/n+-Si and...

Formation of cobalt silicided shallow junction using implant into/through silicide technology and low temperature furnace annealing

This work investigates the shallow CoSi/sub 2/ contacted junctions formed by BF/sub 2//sup +/ and As/sup +/ implantation, respectively, into/through cobalt silicide followed by low temperature furnace annealing. For p/sup +/n junctions fabricated by 20 keV BF/sub 2//sup +/ implantation to a dose of 5/spl times/10/sup 15/ cm/sup -2/, diodes with a leakage current density less than 2 nA/cm/sup 2/ at 5 V reverse bias can be achieved by a 700/spl deg/C/60 min annealing. This diode has a junction depth less than 0.08 /spl mu/m measured from the original silicon surface. For n/sup +/p junctions fabricated by 40 keV As/sup +/ implantation to a dose of 5/spl times/10/sup 15/ cm/sup -2/, diodes with a leakage current density less than 5 nA/cm/sup 2/ at 5 V reverse bias can be achieved by a 700/spl deg/C/90 min annealing; the junction depth is about 0.1 /spl mu/m measured from the original silicon surface. Since the As/sup +/ implanted silicide film exhibited degraded characteristics, an additional fluorine implantation was conducted to improve the stability of the thin silicide film. The fluorine implantation can improve the silicide/silicon interface morphology, but it also introduces extra defects. Thus, one should determine a tradeoff between junction characteristics, silicide film resistivity, and annealing temperature.

Formation of cobalt‐silicided p+n junctions using implant through silicide technology

This paper investigates electrical and material properties of cobalt silicided p+n junctions fabricated using implant through silicide (ITS) technology. The annealing procedure was carried out in an open‐tube furnace with flowing nitrogen. To prevent residual oxygen in the furnace from reacting with the cobalt, a passivating film of molybdenum was used during the initial stage of annealing. BF2+ ion implantation was employed for the p+n junction formation. The ITS scheme and the subsequent annealing conditions were evaluated by analysis of the material properties and investigation of the electrical characteristics of the silicided junctions. During high‐temperature annealing (≥900u2009°C), Co silicide releases its high surface energy via silicon precipitation and film agglomeration. High‐temperature stability of the Co silicide can be improved by BF2+ ion implantation, as indicated by the retardation of film agglomeration and decreased degradation of sheet resistance. Cobalt‐silicided p+n junction diodes with...

Formation of PtSi‐contacted p+n shallow junctions by BF+2 implantation and low‐temperature furnace annealing

This work investigates the characteristics of PtSi‐silicided p+n shallow junctions fabricated by implanting BF+2 ions into either the Pt/Si (ITM scheme) or the PtSi/Si (ITS scheme) structure followed by annealing in N2 furnace at temperatures from 650 to 800u2009°C. For a structure with Pt film of 30 nm thickness or PtSi film of 60 nm thickness, the implantation energy ranges from 40 to 80 keV with a dose ranging from 1×1015 to 1×1016 cm−2. For the ITS samples with BF+2 implantation at 40 keV, all ions are confined in the PtSi layer; therefore, only a modified Schottky junction is formed by the diffusion of boron atoms from the PtSi film during the annealing. The junction depth may be as shallow as 30 nm from the PtSi/Si interface. A complete p+n junction is formed for the ITM samples with implantation at 40 keV as well as all the samples implanted at 80 keV. The junction thus obtained has a forward ideality factor lower than 1.02 and a reverse current density less than 0.2 nA/cm2 at −5 V. Activation energy m...

High‐temperature stability of platinum silicide associated with fluorine implantation

High‐temperature stability of the F+‐ or BF+2 ‐implanted PtSi thin film was investigated. For the PtSi films that received F+ implantation, the film characteristics remain unchanged even after annealing at 800u2009°C for 90 min, while for those without F+ implantation, the film properties begin to degrade after annealing at 750u2009°C as observed by scanning electron microscopic inspection, Auger electron spectroscopy analysis, Rutherford backscattering spectroscopy analysis, and sheet resistance measurement. The secondary ion mass spectroscopy analysis indicates that the fluorine atoms are segregated to the PtSi/Si interface. A fluorine barrier model is proposed to explain the absence of Pt in‐diffusion induced deterioration for the F+‐implanted PtSi film.

Effect of fluorine incorporation on the thermal stability of PtSi/Si structure

It was observed that the fluorine incorporation from ion implantation improved the high-temperature stability of a PtSi/Si structure. The optimum implantation energy was determined to be the energy at which the maximum percentage of the as-implanted fluorine ion locates at the PtSi/Si interface region. SIMS analysis shows that the fluorine atom piles up at the PtSi/Si interface. XPS analysis indicates that the fluorine atoms at the PtSi/Si interface are bonded to the silicon atoms in a form of SiF/sub 2/ or SiF/sub 3/. A fluorine-buffer model is proposed to explain the effect of fluorine incorporation. It is postulated that the Si-F layer acts as a buffer layer to change the PtSi/Si interface energy and preserve the integrity of the silicide layer at high temperature. Fluorinated Schottky junctions were fabricated and the electrical characteristics show that the sustainable process temperature can be improved from 650 degrees C for the unfluorinated junctions to higher than 800 degrees C for the fluorinated junctions. >

Auger recombination-enhanced hot carrier degradation in nMOSFETs with a forward substrate bias

Enhanced hot carrier degradation in nMOSFETs with a forward substrate bias is observed. The degradation cannot be explained by conventional channel hot electron effects. Instead, an Auger recombination-assisted hot electron process is proposed. In the process, holes are injected from the forward-biased substrate and provide for Auger recombination with electrons in the channel, thus substantially increasing channel hot electron energy. Measured hot electron gate current and the light emission spectrum provide evidence that the high-energy tail of channel electrons is increased with a positive substrate bias. The drain current degradation is about ten times more serious in forward-biased substrate mode than in standard mode. The Auger-enhanced degradation exhibits positive temperature dependence and may appear to be a severe reliability issue in high temperature operation condition.

Low‐temperature reaction of thin‐film platinum (≤300 Å) with (100) silicon

Thin platinum films of 164 and 303 A thickness are deposited on (100) silicon and annealed at temperatures ranging from 180 to 300u2009°C in a nitrogen furnace for various times ranging from 1 min to 200 h. Sheet resistance (Rs ) measurement shows a four‐stage silicide formation sequence: (1) the Rs increases to a maximum value; (2) the Rs then decreases to a minimum value; (3) the Rs increases once again and reaches a second maximum value; and (4) the Rs decreases to a final stable value. X‐ray diffraction analysis indicates that the initial phase grown is Pt12Si5 which corresponds to the sheet‐resistance increase in the first stage. This phase is also identified by the transmission electron diffraction analysis. This is the first time that the Pt12Si5 phase formed by the Pt/Si direct reaction is observed. The second stage corresponds to the growth of Pt2Si as confirmed by the x‐ray diffraction and Auger spectroscopy analyses. The third stage corresponds to the growth of PtSi and the final stage corresponds ...

Formation of n+p shallow junction by As+ implantation through CoSi2 film

Junction formation by As+ ion implantation into CoSi2 and subsequent drive‐in annealing was investigated. Diodes with a leakage current density of 0.4 nA/cm2 at 5 V reverse bias can be obtained by a 700u2009°C/90 min furnace annealing. The performance of junction is mainly determined by the annealing temperature and time as well as the implantation dose. The implantation energy only has a minor effect on junction properties. Based on the experimental results, we define an appropriate process window for this junction formation technique.