Rapid thermal annealing of si implanted gaas

Rapid thermal annealing (RTA) technology offers potential advantages for GaAs MESFET device technology such as reducing dopant diffusion and minimizing the redistribution of background impurities. LEC semi-insulating GaAs substrates were implanted with Si at energies from 100 to 400 keV to doses from 1 × 10¹² to 1 × 10¹⁴/cm². The wafers were encapsulated with Si₃N₄ and then annealed at temperatures from 850-1000° C in a commercial RTA system. Wafers were also annealed using a conventional furnace cycle at 850° C to provide a comparison with the RTA wafers. These implanted layers were evaluated using capacitance-voltage and Hall effect measurements. In addition, FET’s were fabricated using selective implants that were annealed with either RTA or furnace cycles. The effects of anneal temperature and anneal time were determined. For a dose of 4 × 10¹²/cm² at 150 keV with anneal times of 5 seconds at 850, 900, 950 and 1000° C the activation steadily increased in the peak of the implant with overlapping profiles in the tail of the profiles, showing that no significant diffusion occurs. In addition, the same activation could be obtained by adjusting the anneal times. A plot of the equivalent anneal times versus 1/T gives an activation energy of 2.3 eV. At a higher dose of 3 × 10¹³ an activation energy of 1.7 eV was obtained. For a dose of 4 × 10¹² at 150 keV both the RTA and furnace annealing give similar activations with mobilities between 4700 and 5000 cm²/V-s. Mobilities decrease to 4000 at a dose of 1 × 10¹³ and to 2500 cm²/V-s at 1 × 10¹⁴/cm². At doses above 1 × 10¹³ the RTA cycles gave better activation than furnace annealed wafers. The MESFET parameters for both RTA and furnace annealed wafers were nearly identical. The average gain and noise figure at 8 GHz were 7.5 and 2.0, respectively, for packaged die from either RTA or furnace annealed materials.     

Low resistance bilayer Nd/Al ohmic contacts on n-type GaN

A bilayer Nd/Al metallization structure has been deposited onto low pressure organometallic vapor phase epitaxy grown n-type GaN ( 1 × 10¹⁸ cm⁻³) by electron-beam evaporation. Ohmic metal contacts were patterned photolithographically for standard transmission line measurement, and then thermally annealed at temperatures ranging from 200 to 350°C and from 500 to 650°C using conventional thermal annealing (CTA) and rapid thermal annealing (RTA), respectively. The lowest values for the specify contact resistivity of 9.8 × 10⁻⁶ Ω−cm² and 8 × 10⁻⁶ Ω−cm² were obtained using Nd/Al metallization with CTA of 250°C for 5 min and RTA of 600°C for 30 s. Examination of the surface morphology using atomic force microscopy as a function of annealing temperature revealed that the surface roughness was strongly influenced by conventional thermal annealing, it was smooth in the temperature range from 550 to 650°C for rapid thermal annealing. Auger electron spectroscopy depth profiling was employed to investigate the metallurgy and interdiffusion of contact formation.     

Activation efficiencies for a standard qualification implant in gaas annealed by a rapid thermal process

Recently a 150 keV, 2 × 10¹² cm⁻², Si²⁹ implant, with furnace annealing at 850° C for 10 min with a GaAs proximity wafer, has been proposed as a standard qualification test for semi-insulating GaAs. In general, the electrical activation efficiency of implanted wafers is determined either from Hall effect data or from capacitance-voltage (C-V) data; however, the Hall effect method requires sizable depletion corrections at low implant doses. In this paper, we examine the proposed standard, and the methods of determining activation, from three points of view: (1) rapid-thermal annealing (RTA) vs furnace annealing; (2) a Si proximity cap vs a GaAs proximity cap; and (3) Hall effect vs C-V. Our conclusions are: (1) RTA produces higher activation efficiencies, at least for our particular wafers, than furnace annealing; (2) Si and GaAs proximity caps produce nearly equivalent activation efficiencies; and (3) the Hall effect, when corrected for depletion, is a useful technique for measuring activation efficiency, and appears to be more accurate than the C-V technique.     

Temperature-Dependent Studies of Si-Implanted Al<Subscript>0.33</Subscript>Ga<Subscript>0.67</Subscript>N with Different Annealing Temperatures and Times

Electrical activation studies were carried out on Si-implanted Al_0.33Ga_0.67N as a function of ion dose, annealing temperature, and annealing time. The samples were implanted at room temperature with Si ions at 200 keV in doses ranging from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁵ cm⁻², and subsequently proximity-cap annealed from 1150°C to 1350°C for 20 min to 60 min in a nitrogen environment. One hundred percent electrical activation efficiency was obtained for Al_0.33Ga_0.67N samples implanted with a dose of 1 × 10¹⁵ cm⁻² after annealing at either 1200°C for 40 min or at 1300°C for 20 min. The samples implanted with doses of 1 × 10¹⁴ cm⁻² and 5 × 10¹⁴ cm⁻² exhibited significant activations of 74% and 90% after annealing for 20 min at 1300°C and 1350°C, respectively. The mobility increased as the annealing temperature increased from 1150°C to 1350°C, showing peak mobilities of 80 cm²/V s, 64 cm²/V s, and 61 cm²/V s for doses of 1 × 10¹⁴ cm⁻², 5 × 10¹⁴ cm⁻², and 1 × 10¹⁵ cm⁻², respectively. Temperature-dependent Hall-effect measurements showed that most of the implanted layers were degenerately doped. Cathodoluminescence measurements for all samples exhibited a sharp neutral donor-bound exciton peak at 4.08 eV, indicating excellent recovery of damage caused by ion implantation.     

High-Dose Phosphorus-Implanted 4H-SiC: Microwave and Conventional Post-Implantation Annealing at Temperatures ≥1700°C

Semi-insulating 4H-SiC ⟨0001⟩ wafers have been phosphorus ion implanted at 500°C to obtain phosphorus box depth profiles with dopant concentration from 5 × 10¹⁹ cm⁻³ to 8 × 10²⁰ cm⁻³. These samples have been annealed by microwave and conventional inductively heated systems in the temperature range 1700°C to 2050°C. Resistivity, Hall electron density, and Hall mobility of the phosphorus-implanted and annealed 4H-SiC layers have been measured in the temperature range from room temperature to 450°C. The high-resolution x-ray diffraction and rocking curve of both virgin and processed 4H-SiC samples have been analyzed to obtain the sample crystal quality up to about 3 μm depth from the wafer surface. For both increasing implanted phosphorus concentration and increasing post-implantation annealing temperature the implanted material resistivity decreases to an asymptotic value of about 1.5 × 10⁻³ Ω cm. Increasing the implanted phosphorus concentration and post-implantation annealing temperature beyond 4 × 10²⁰ cm⁻³ and 2000°C, respectively, does not bring any apparent benefit with respect to the minimum obtainable resistivity. Sheet resistance and sheet electron density increase with increasing measurement temperature. Electron density saturates at 1.5 × 10²⁰ cm⁻³ for implanted phosphorus plateau values ≥4 × 10²⁰ cm⁻³, irrespective of the post-implantation annealing method. Implantation produces an increase of the lattice parameter in the bulk 4H-SiC underneath the phosphorus-implanted layer. Microwave and conventional annealing produce a further increase of the lattice parameter in such a depth region and an equivalent recovered lattice in the phosphorus-implanted layers.     

P-type doping of GaAs by carbon implantation

The electrical properties of C-implanted <100> GaAs have been studied following rapid thermal annealing at temperatures in the range from 750 to 950°C. This includes dopant profiling using differential Hall measurements. The maximum p-type activation efficiency was found to be a function of C-dose and annealing temperature, with the optimum annealing temperature varying from 900°C for C doses of 5 × 10¹³ cm⁻² to 800°C for doses ≥5 × 10¹⁴cm⁻². For low dose implants, the net p-type activation efficiency was as high as 75%; while for the highest dose implants, it dropped to as low as 0.5%. Moreover, for these high-dose samples, 5 × 10¹⁵ cm⁻², the activation efficiency was found to decrease with increasing annealing temperature, for temperatures above ∼800°C, and the net hole concentration fell below that of samples implanted to lower doses. This issue is discussed in terms of the amphoteric doping behavior of C in GaAs. Hole mobilities showed little dependence on annealing temperature but decreased with increasing implant dose, ranging from ∼100 cm²/V·s for low dose implants, to ∼65 cm²/V·s for high dose samples. These mobility values are the same or higher than those for Be-, Zn-, or Cd-implanted GaAs.     

Optical and Magnetic Properties of ZnO:V Prepared by Ion Implantation

We report on the optical and magnetic properties of the magnetic semiconductor Zn(V)O fabricated by implantation of 195 keV ₅₁V⁺ ions into bulk ZnO:Al grown by a hydrothermal technique. Two sets of the samples, containing N _d –N _a ∼ 10¹⁵ cm⁻³ and 10¹⁸ cm⁻³, were implanted to doses of 1 × 10¹⁵ cm⁻², 3 × 10¹⁵ cm⁻², and 1 × 10¹⁶ cm⁻². The ion implantation was performed at 573 K. To remove irradiation-induced defects, the samples were annealed in air at 1073 K. Photoluminescence (PL) measurements of Zn(V)O films were carried out at temperatures from 10 K to 300 K. The effects of implantation dose and free carrier concentration on the magnetic properties of Zn(V)O were studied using a superconducting quantum interference device magnetometer. Ferromagnetism has been observed in annealed highly conductive samples implanted to 1 × 10¹⁶ cm⁻². The PL studies of ZnO bulk samples implanted with V⁺ have revealed that thermal annealing at 1073 K restores to a large extent the optical quality of the material. A new emission line centered at 3.307 eV has been found in the PL spectrum of the highly conductive samples implanted to the dose of 1 × 10¹⁶ cm⁻², which is most probably due to complexes involving V ions.     

Si-implantation into GaAs grown on Si

200 keV Si implantations were performed in the dose range of 5 × 10¹² − 1 × 10¹⁴ cm⁻² in GaAs grown on Si. For comparison implants were also performed in GaAs layers grown on GaAs substrates. Implanted layers were annealed by both furnace and halogen lamp rapid thermal anneals. Significantly lower donor activations were observed in GaAs layers grown on Si substrates than in the layers grown on GaAs substrates. Extremely low dopant activations were obtained for Be implants in GaAs grown on Si. Photoluminescence and photoreflectance measurements were also performed on the implanted material.     

Fluorine behavior in BF 2 + implanted polysilicon films subjected to rapid thermal annealing

The physical and electrical properties of BF ₂ ⁺ implanted polysilicon films subjected to rapid thermal annealing (RTA) are presented. It is found that the out diffusion ofF and its segregation at polysilicon/silicon oxide interface during RTA are the major causes ofF anomalous migration. Fluorine bubbles were observed in BF ₂ ⁺ implanted samples at doses of 1×10¹⁵ and 5×10¹⁵ cm⁻² after RTA.     

Rapid capless annealing of28Si,64Zn,and9Be implants in GaAs

We report the use of tungsten-halogen lamps for rapid (−10 s) thermal annealing of ion-implanted (100) GaAs under AsH₃/Ar and N₂ atmospheres. Annealing under flowing AsH₃/Ar was carried out without wafer encapsulation. Rapid capless annealing activated implants in GaAs with good mobility and surface morphology. Typical mobilities were 3700–4500 cm²/V-s for n-layers with about 2×10¹⁷cm⁻³ carrier concentration and 50–150 cm²/v-s for 0.1–5xl0¹⁹ cm⁻³ doped p-layers. Rapid thermal annealing was performed in a vertical quartz tube where different gases (N₂, AsH₃/H₂, AsH₃/Ar) can be introduced. Samples were encapsulated with SiO when N₂ was used. Tungsten-halogen lamps of 600 or 1000 W were utilized for annealing GaAs wafers ranging from 1 to 10 cm² in area and 0.025 to 0.040 cm in thickness. The transient temperature at the wafer position was monitored using a fine thermocouple. We carried out experiments for energies of 30 to 200 keV, doses of 2×10¹² to 1×10¹⁵ cm⁻², and peak temperatures ranging from 600 to 1000‡C. Most results quoted are in the 700 to 870‡C temperature range. Data on implant conditions, optimum anneal conditions, electrical characteristics, carrier concentration profiles, and atomic profiles of the implanted layers are described. Presented at the 25th Electronic Materials Conference, Burlington, VT, June 22, 1983.     

Surface roughening in ion implanted 4H-silicon carbide

Silicon carbide (SiC) devices have the potential to yield new components with functional capabilities that far exceed components based on silicon devices. Selective doping of SiC by ion implantation is an important fabrication technology that must be completely understood if SiC devices are to achieve their potential. One major problem with ion implantation into SiC is the surface roughening that results from annealing SiC at the high temperatures which are needed to activate implanted acceptor ions, boron or aluminum. This paper examines the causes and possible solutions to surface roughening of implanted and annealed 4H-SiC. Samples consisting of n-type epilayers (5 × 10¹⁵ cm⁻³, 4 μm thick) on 4H-SiC substrates were implanted with B or Al to a total dose of 4 × 10¹⁴ cm⁻² or 2 × 10¹⁵ cm⁻², respectively. Roughness measurements were made using atomic force microscopy. From the variation of root mean square (rms) roughness with annealing temperature, apparent activation energies for roughening following implantation with Al and B were 1.1 and 2.2 eV, respectively, when annealed in argon. Time-dependent activation and surface morphology analyses show a sublinear dependence of implant activation on time; activation percentages after a 5 min anneal following boron implantation are about a factor of two less than after a 40 min anneal. The rms surface roughness remained relatively constant with time for anneals in argon at 1750°C. Roughness values at this temperature were approximately 8.0 nm. Annealing experiments performed in different ambients demonstrated the benefits of using silane to maintain good surface morphology. Roughnesses were 1.0 nm (rms) when boron or aluminum implants were annealed in silane at 1700°C, but were about 8 and 11 nm for B and Al, respectively, when annealed in argon at the same temperature.     

Nearly Perfect Electrical Activation Efficiencies from Silicon-Implanted Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N with High Aluminum Mole Fraction

Electrical activation studies of Al _x Ga_1−x N (x = 0.45 and 0.51) implanted with Si for n-type conductivity have been made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁵ cm⁻² at room temperature. The samples were subsequently annealed from 1150°C to 1350°C for 20 min in a nitrogen environment. Nearly 100% electrical activation efficiency was successfully obtained for the Si-implanted Al_0.45Ga_0.55N samples after annealing at 1350°C for doses of 1 × 10¹⁴ cm⁻² and 5 × 10¹⁴ cm⁻² and at 1200°C for a dose of 1 × 10¹⁵ cm⁻², and for the Al_0.51Ga_0.49N implanted with silicon doses of 1 × 10¹⁴ cm⁻² and 5 × 10¹⁴ cm⁻² after annealing at 1300°C. The highest room-temperature mobility obtained was 61 cm²/V s and 55 cm²/V s for the low-dose implanted Al_0.45Ga_0.55N and Al_0.51Ga_0.49N, respectively, after annealing at 1350°C for 20 min. These results show unprecedented activation efficiencies for Al _x Ga_1−x N with high Al mole fractions and provide suitable annealing conditions for Al _x Ga_1−x N-based device applications.     

Surface condition of Si implanted GaAs revealed by the noncontact laser/microwave method

The surface recombination of GaAs which has a heavily doped surface layer formed by Si implantation and subsequent annealing has been investigated using the noncontact laser/microwave evaluation method. The experimental results of the samples implanted with doses ranging from 1.0 × 10¹¹ to 3.9 × 10¹² cm⁻² at an energy of 100 keV indicate that the effective surface recombination velocity decreases with dosage because of the heavily doped layer formed after the annealing. On the other hand, the results of the samples implanted with a dose of 3.9 × 10¹² cnr⁻² at energies raging from 50 to 180 keV indicate that the effective surface recombination velocity increases with energy. This is mainly due to the decrease in the peak carrier concentration in the heavily doped layer.     

Analysis of ion beam induced damage and amorphization of 6H-SiC by raman scattering

Raman scattering analysis of damaged SiC layers obtained by 200 keV Ge⁺ ion implantation into 6H-SiC has been performed as a function of the implanted dose (up to 10¹⁵ cm⁻²) and annealing temperature (up to 1500°C). The results obtained show the presence of three different damage levels: low damage level (doses ≤3 × 10¹² cm⁻²), medium to high damage level (doses between 10¹³ and 10¹⁴ cm^-2), and formation of a continuous amorphous layer for doses higher than the amorphization threshold of 2–3 × 10¹⁴ cm⁻². Moreover, at doses of about 10¹⁴ cm⁻² (below the amorphization threshold) amorphous domains are already observed. The Raman spectra indicate the existence of structural differences between the amorphous phase at doses below and above the threshold. After annealing, there is a residual damage which cannot be removed even at the highest annealing temperature of 1500°C. Differences in residual damage between the samples implanted at doses of 10¹⁴ and 10¹⁵ cm^-2 and annealed at the highest temperatures are observed from the peaks in the 1000–1850 cm^-1 spectral region. Finally, annealing at the highest temperature is required to observe the complete disappearance of the amorphous bands.     

Effect of annealing temperature on 1.5 μm photoluminescence from Er-lmplanted 6H-SiC

The effect of post-implantation anneal on erbium-doped 6H-SiC has been investigated. 6H-SiC has been implanted with 330 keV Er⁺ at a dose of 1 × 1013 /cm2. Er depth profiles were obtained by secondary ion mass spectrometry (SIMS). The as-implanted Er-profile had a peak concentration of∼1.3 × 10¹⁸/cm³ at a depth of 770Å. The samples were annealed in Ar at temperatures from 1200 to 1900°C. The photoluminescence intensity integrated over the 1.5 to 1.6 μm region is essentially independent of annealing temperature from 1400 to 1900°C. Reduced, but still significant PL intensity, was measured from the sample annealed at 1200°C. The approximate diffusivity of Er in 6H SiC was calculated from the SIMS profiles, yielding values from 4.5 × 10⁻¹⁶ cm²/s at 1200°C to 5.5 × 10⁻¹⁵ cm²/s at 1900°C.     

Internal-getter formation in nitrogen-doped dislocation-free silicon wafers

An experimental study is reported concerning the formation of defects in nitrogen-doped dislocation-free silicon wafers under a multistage heat treatment to produce an internal getter, the first stage being rapid thermal annealing (RTA) under different conditions. The experiments are conducted on p-Si(100) wafers of diameter 200 mm with an oxygen content of (6−7) × 10¹⁷ cm⁻³ and a doping level of 1.6 × 10¹⁴ cm⁻³, the resistivity being 10–12 ω cm. The processed wafers are examined by optical microscopy and transmission electron microscopy. With normal conditions of RTA (argon, 1250°C, 20 s), the process is found to be incapable of creating a defect-free subsurface layer of adequate thickness, though it is able to provide the desired system of defects in the bulk. The aim is achieved by changing to sequential RTA in oxygen and argon as the first stage. The reasons for the results are presented.     

Redistribution of implanted dopants in GaN

Donor (S, Se, and Te) and acceptor (Mg, Be, and C) dopants have been implanted into GaN at doses of 3–5×10¹⁴ cm⁻² and annealed at tem peratures up to 1450°C. No redistribution of any of the elements is detectable by secondary ion mass spectrometry, except for Be, which displays behavior consistent with damageassisted diffusion at 900°C. At higher temperatures, there is no further movement of the Be, for peak annealing temperature durations of 10 s. Effective diffusivities are ≤2×10⁻¹³ cm²·s⁻¹ at 1450°C for each of the dopants in GaN.     

MeV energy sulfur implantation in GaAs and InP

Room temperature and elevated temperature sulfur implants were performed into semi-insulating GaAs and InP at variable energies and fluences. The implantations were performed in the energy range 1–16 MeV. Range statistics of sulfur in InP and GaAs were calculated from the secondary ion mass spectrometry atomic concentration depth profiles and were compared with TRIM92 values. Slight in-diffusion of sulfur was observed in both InP and GaAs at higher annealing temperatures for room temperature implants. Little or no redistribution of sulfur was observed for elevated temperature implants. Elevated temperature implants showed higher activations and higher mobilities compared to room temperature implants in both GaAs and InP after annealing. Higher peak electron concentrations were observed in sulfur-implanted InP (n ≈ 1 × 10¹⁹ cm⁻³) compared to GaAs (n ≈ 2 × 10¹⁸ cm⁻³). The doping profile for a buried n⁺ layer (n ≈ 3.5 × 10¹⁸ cm⁻³) of a positive-intrinsic-negative diode in GaAs was produced by using Si/S coimplantation.     

A technique to reduce the contact resistance to 4H-silicon carbide using germanium implantation

The effects of implanted Ge on the resistance of nickel-metal contacts to n-type and p-type 4H-SiC are reported. The Ge was implanted with an energy of 346 keV and a dose of 1.7×10¹⁶ cm⁻², and the wafer was annealed up to 1700°C for 30 min. Contact resistance measurements using the transfer length method (TLM) were performed on etched mesas of n-type and p-type 4H-SiC, with and without the Ge. For the annealed-Ni metal contacts, the Ge lowered the specific contact resistivity from 5.3×10⁻⁴ Ωcm² to 6.0×10⁻⁵ Ωcm² for n-type SiC and from 1.2×10⁻³ Ωcm² to 8.3×10⁻⁵ Ωcm² for p-type SiC. For the as-deposited (unannealed) Ni, the Ge produced ohmic contacts, whereas the contacts without Ge were rectifying. These results suggest that the addition of Ge can be an important process step to reduce the contact resistance for SiC-device applications.     

DEEP LEVEL DEFECTS IN SI-IMPLANTED LEC UNDOPED Si-GaAs

The residual electrically active defects in(4×10~(12)cm~(-2)(30KeV)+5×10~(12)cm~(-2)(130KeV))si-implanted LEC undoped si-GaAs activated by two-step rapid thermal annealing(RTA)LABELED AS 970℃(9S)+750℃(12S)have been investigated with deep level transient spec-troscopy(DLTS).Two electron traps ET_1(E_c-0.53eV,σ_n=2.3×10~(-16)cm~2)and ET_2(E_c-0.81eV,σ_n=9.7×10(-13)cm~2)are detected.Furthermore,the noticeable variations of trap's con-centration and energy level in the forbidden gap with the depth profile of defects induced by ion im-plantation and RTA process have also been observed.The[As_i·V_(As)·As_(Ga)]and[V_(As)·As_i·V_(Ga)·As_(Ga)]are proposed to be the possible atomic configurations of ET_1 and ET_2,respectively to explaintheir RTA behaviors.