Shallow Junction Formation Research Articles

Shallow junction formation via lateral boron autodoping during rapid thermal process

Autodoping is a well-known phenomenon of unwanted dopant transfer in silicon epitaxy process. In this work, we discovered boron lateral autodoping in normal rapid thermal process (RTP) and used it to controllably form shallow junctions for device fabrication. The redeposition of boron from the gas phase to the solid surface was identified to be the limiting step of the boron incorporation into the undoped silicon area in the RTP process. At a given RTP temperature, boron autodoping could be increased by elevating the concentration of the boron source or enhancing the evaporation coefficient. Extending the annealing time can substantially improve the uniformity of the boron concentration in the gas phase, thus reducing the pattern dependence of the autodoping results. In addition, the autodoping process also avoids the traps and defects induced by ion implantation. Therefore, the described mechanism holds great promise for shallow junction formation in selectively patterned area with low cost.

Formation of Highly-Activated N-Type Shallow Junction in Germanium Using Nanosecond Laser Annealing and Fluorine Co-Doping

By employing a 355-nm nanosecond (ns) ultraviolet (UV) laser annealing, the impact of fluorine (F) co-doping on the formation of a highly activated N-type shallow junction in germanium (Ge) is investigated. Secondary ion mass spectrometry (SIMS) depth profiling of phosphorus (P) demonstrated that an ultra high P concentration of 9 × 1020 cm−3 at a shallow junction of 55 nm with less dopant diffusion can be obtained using ns laser annealing. F co-doping was confirmed to be an efficient way to improve the activation of the P dopants, but show less influence on the redistribution of P dopants within the NLA melted region. However, the activation level of the shallow junction could be increased to approximately 1 × 1020 cm−3 in the presence of F at an optimized concentration.

Conformal and Ultra Shallow Junction Formation Achieved Using a Pulsed-Laser Annealing Process Integrated With a Modified Plasma Assisted Doping Method

Recently, a shallow and conformal doping profile is required for promising 3D structured devices. In this study, we deposited the dopant phosphorus (P) using modified plasma assisted doping (PaD) followed by an annealing process to electrically activate the dopants. A rapid thermal annealing process (RTP) was the first approach tested for activation but it resulted in a deep junction (>35 nm). To reduce the junction depth, we tried the flash lamp annealing process (FLP) to shorten the annealing time. We also predicted the annealing temperature by numerical thermal analysis, which reached 1,020 °C. However, the FLP resulted in a deep junction (~ 30 nm), which was not shallow enough to suppress short channel effects. Since an even shorter annealing process was required to form a ultra-shallow junction, we tried the laser annealing process (LAP) as a promising alternative. The LAP, which had a power density of 0.3 J/cm2, increased the surface temperature up to 1,100 °C with a shallow isothermal layer. Using the LAP, we achieved a USJ with an activated surface dopant concentration of $3.86\times 10 ^{19}$ cm−3 and a junction depth of 10 nm, which will allow further scaling-down of devices.

Study of n-type doping in germanium by temperature based PF+ implantation

Incorporation of P in germanium was studied by using PF+ molecular implantation in a range from room temperature to 400 °C. The presence of F acted as a barrier for P in-diffusion and resulted in higher activation of P at room temperature. In addition, it is found that when the implantation is performed at 400 °C, the residual defects are stable and the diffusion of P can be blocked during activation annealing. Therefore, the final junction depth could be well controlled by the implantation process itself. This method is meaningful for the shallow junction formation in sub 14-nm Ge-based FinFETs or high-performance photodetectors.

Formation and Characterization of Shallow Junctions in GaAs Made by Ion Implantation and ms‐Range Flash Lamp Annealing

With the demand of aggressive scaling in nanoelectronics, further progress can be realized by integration of high mobility semiconductors, such as III–V compound semiconductors, with complementary metal‐oxide‐semiconductor (CMOS) technology. In this study, the formation of shallow n–p and p–n junctions in GaAs utilizing ion implantation of S and Zn, respectively, followed by millisecond‐range flash lamp annealing (FLA) is presented. The distribution of implanted elements obtained by secondary ion mass spectrometry (SIMS) shows that the FLA process can effectively suppress the diffusion of dopants. Simultaneously, the ms‐range annealing is sufficient to recrystallize the implanted layer and to activate the dopants. Formation of p–n and n–p junctions is confirmed by current–voltage characteristics. The ratio of reverse to forward current can reach up to 1.7 × 107 in the n‐GaAs:Zn case.

A Novel Solar Cell Shallow Emitter Formation Process by Ion-Implantation and Dopant Modulation Through Surface Chemical Etching

Ion-implantation is an advanced technology to inject dopants for shallow junction formation. Due to the ion-induced sputtering effect at low implant energy where dopants tend to accumulate at the silicon surface, the excess ion doses can be easily removed via a surface chemical wet etching process. By taking advantage of the dose limitation characteristic, we proposed a novel method to form shallow emitters with various dopant densities. Two integration flows have been investigated: (1) wet etch after implantation before junction anneal and (2) wet etch after implantation and junction anneal. The two integration flows observed a difference in the density of doping impurities during the thermal process, which is related to the substrate recombination rates. Selective emitter (SE) structures with the two types of integration flows were characterized. Comparing the blanket emitter and SE structures with two types of etching methods, the device with wet etch before annealing process achieved the best effective carrier lifetime of 53.05 μs, which leads to a higher short circuit current density. Hence, this SE cell demonstrated a better blue response and shows an improvement in the conversion efficiency.

Germanium Junctions for Beyond-Si Node Using Flash Lamp Annealing (FLA)

ABSTRACTWe report on the formation of shallow junctions with high activation in both n+/p and p+/n Ge junctions using ion implantation and Flash Lamp Annealing (FLA). The shallowest junction depths (Xj) formed for the n+/p and p+/n junctions were 7.6 nm and 6.1 nm with sheet resistances (Rs) of 860 ohms/sq. and 704 ohms/sq., respectively. By reducing knocked-on oxygen during ion implantation in the n+/p junctions, Rs was decreased by between 5% and 15%. The lowest Rs observed was 235 ohms/sq. with a junction depth of 21.5 nm. Hall measurements clearly revealed that knocked-on oxygen degraded phosphorus activation (carrier concentration). In the p+/n Ge junctions, we show that ion implantation damage induced high boron activation. Using this technique, Rs can be reduced from 475 ohms/sq. to 349 ohms/sq. These results indicate that the potential for forming ultra-shallow n+/p and p+/n junctions in the nanometer range in Ge devices using FLA is very high, leading to realistic monolithically-integrated Ge CMOS devices that can take us beyond Si technology.

Diffusion and recrystallization of B implanted in crystalline and pre-amorphized Ge in the presence of F

Although the diffusion control and dopant activation of Ge p-type junctions are straightforward when using B+ implantation, the use of the heavier BF2+ ions or even BF+ is still favored in terms of shallow junction formation and throughput—because implants can be done at higher energies, which can give higher beam currents and beam stability—and thus the understanding of the effect of F co-doping becomes important. In this work, we have investigated diffusion and end-of-range (EOR) defect formation for B+, BF+, and BF2+ implants in crystalline and pre-amorphized Ge, employing rapid thermal annealing at 600 °C and 800 °C for 10 s. It is demonstrated that the diffusion of B is strongly influenced by the temperature, the presence of F, and the depth of amorphous/crystalline interface. The B and F diffusion profiles suggest the formation of B–F complexes and enhanced diffusion by interaction with point defects. In addition, the strong chemical effect of F is found only for B in Ge, while such an effect is vanishingly small for samples implanted with F alone, or co-implanted with P and F, as evidenced by the high residual F concentration in the B-doped samples after annealing. After 600 °C annealing for 10 s, interstitial-induced compressive strain was still observed in the EOR region for the sample implanted with BF+, as measured by X-ray diffraction. Further analysis by cross-sectional transmission electron microscopy showed that the {311} interstitial clusters are the majority type of EOR defects. The impact of these {311} defects on the electrical performance of Ge p+/n junctions formed by BF+ implantation was evaluated.

(Invited) Pattern and Emissivity Insensitive Dopant Activation and Silicide Contact Formation Annealing in a Hot Wall Rapid Thermal Annealing System

Rapid thermal annealing (RTA) enabled shallow junction formation requires very short time annealing at high temperatures for low thermal budget. RTA is typically done by lamp-based radiant heating. Radiant power from lamp arrays is close-loop controlled to execute the temperature of the Si wafer as programmed. The increase of annealing temperature and the decrease of annealing time are generally required for more aggressive device scaling. However, the use of non-equilibrium radiant heat sources (photon energy from lamp arrays) makes the heating process sensitive to the optical properties of the Si wafers. Local temperature non-uniformity during RTA is considered an important contributor for within-die process variations which cause significant problems for advanced complimentary metal-oxide-semiconductor (CMOS) device manufacturing. RTA-induced variations strongly depend on circuit layout patterns and optical properties of exposed materials on the surface of the Si wafers. This phenomenon is often referred to as “pattern effect” known from the early days of RTA introduction in the semiconductor industry. In efforts to reduce the “pattern effect”, various approaches have been proposed and implemented in device manufacturing. Shielding device patterns from the radiant heat source is a common approach, having limited success. It is done by either placing a dummy wafer on the pattern side of the Si wafer or backside heating. One other common approach is to homogenize the optical properties of the pattern side of Si wafer by either adding an optical absorption layer or dummy patterns. A differential thermal energy control technique is also proposed for pattern effect suppression. Non-radiative heating techniques have been proposed and demonstrated effectiveness of this “pattern effect” suppression. In this paper, various silicide contact formations on implanted single crystalline Si in source/drain region and implanted poly-Si in gate region were studied over wide ranges of RTA temperature and time using a hot wall RTA system which uses mainly natural convection and conduction through ambient gas. Dopant profiles of the silicide and doped Si after silicidation in the hot wall RTA system were characterized. Proposed possible silicide formation and dopant diffusion mechanisms are discussed. Differences between radiant heating and non-radiant heating on the silicide formation and dopant profiles are compared. The pattern and emissivity insensitive dopant activation and silicide contact formation annealing results will be introduced and potential applications of the hot wall RTA technique in advanced CMOS devices will be proposed.

NMOS Low Boron Activation in Pre-Amorphise Silicon

The high demand of smaller and compact size of MOSFETs has leads to desirable for ultra shallow junction formation with low sheet resistance and good electrical performances. These two characteristics are required to suppress short channel effects and to increase the efficiency of device. In this paper, Pre-amorphise implantation (PAI) PMOS with different doses of Boron and the basic PMOS structure are done by using ATHENA and the performance of devices is compared by using ATLAS software package from Silvaco TCAD. Comparison done in electrical characteristic, I-V curve Ion and Ioff has showed PMOS with PAI technology with low boron doses resulted in increasing electrical performance characteristic.

Modeling of junction formation in scaled Si devices

In this article, modeling of junction formation in scaled Si device is shown. An atomistic kinetic Monte Carlo (KMC) diffusion modeling is used for the analysis of dopant diffusion and defects during shallow junction formation processes. Dopant diffusion and defect evolution during sub-millisecond non-melt laser annealing (NLA) are studied in both experiments and an atomistic kMC diffusion modeling. Pre-amorphization implant is often used for ultra shallow junction formation. It is shown that Solid Phase Epitaxial Regrowth (SPER) annealing stage plays an important role for dopant diffusion in junction formation process. As Ge implant energy is increased, damage structure and IV composition of Amorphous Pockets are changed and this affects the dopant diffusion and activation behavior. KMC simulations show that B, As deactivation is induced by the formation of dopant-defect complexes, such as B n I m , As n V m , As n I m , As n , during millisecond annealing time range. Both experiments and KMC show that defect evolution during millisecond annealing time range. Fluorine, Carbon co-implant effects are also modeled using KMC.

Point defect engineering study of phosphorus ion implanted germanium

AbstractWe present experimental results on shallow junction formation in germanium by phosphorus ion implantation and standard rapid thermal processing. An attempt is made to improve phosphorus electrical activation using point defect engineering method by introducing an excess of point defects in germanium prior to the phosphorus implantation. The focus is on studying the phosphorus activation and diffusion as a function of germanium co‐implant energy. Hall Effect and Secondary Ion Mass Spectrometry (SIMS) measurements are employed for characterisation of phosphorus activation and diffusion, respectively. Phosphorus activation was improved at higher annealing temperature for the implants with germanium co‐implant. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

NMOS Performance of Low Boron Activation on Group V for Ultra-Shallow Junction Formation

Fabrication of ultra shallow junctions with low contact resistances is desired to advance current CMOS technology. The low Boron activation on Group V for ultra shallow junction formation will makes the chip fabrication works effectively. SilvacoTCAD (Technology Computer Aided Design) manages simulation tasks and analyzing simulation results when ultra-shallow junction formation is using low-boron activation on Phosphorus, Antimony and Arsenic.A stimulate process like implantation, diffusion and dopant activation and epitaxial growth in different semiconductor materials has been analyzed as well as investigate the effects of energy of boron ion beams on ultra shallow junction formation.As a result, the electrical characteristics of NMOS structure by obtaining graph of IDVGSand IDVDShas been studied when there are variations in junction length (Xj), and gatelength (Lg).

Lithium implantation at low temperature in silicon for sharp buried amorphous layer formation and defect engineering

The crystalline-to-amorphous transformation induced by lithium ion implantation at low temperature has been investigated. The resulting damage structure and its thermal evolution have been studied by a combination of Rutherford backscattering spectroscopy channelling (RBS/C) and cross sectional transmission electron microscopy (XTEM). Lithium low-fluence implantation at liquid nitrogen temperature is shown to produce a three layers structure: an amorphous layer surrounded by two highly damaged layers. A thermal treatment at 400 °C leads to the formation of a sharp amorphous/crystalline interfacial transition and defect annihilation of the front heavily damaged layer. After 600 °C annealing, complete recrystallization takes place and no extended defects are left. Anomalous recrystallization rate is observed with different motion velocities of the a/c interfaces and is ascribed to lithium acting as a surfactant. Moreover, the sharp buried amorphous layer is shown to be an efficient sink for interstitials impeding interstitial supersaturation and {311} defect formation in case of subsequent neon implantation. This study shows that lithium implantation at liquid nitrogen temperature can be suitable to form a sharp buried amorphous layer with a well-defined crystalline front layer, thus having potential applications for defects engineering in the improvement of post-implantation layers quality and for shallow junction formation.

Formation of shallow junctions in gallium and phosphorus compensated silicon for cell performance improvement

Solar cells have been fabricated from gallium and phosphorus compensated Czochralski silicon wafer. It is found that these solar cells have shallower n+p junctions, compared to those based on conventional silicon. The cell efficiencies under 1 sun illumination are on average 0.2% higher than those of conventional solar cells. This improvement is associated with the better spectral response in the short-wavelength range, due to the formation of shallower junctions.

Systematic study of shallow junction formation on germanium substrates

Published results on Ge junctions are benchmarked systematically using R S – X J plots. The electrical activation level required to meet the ITRS targets is calculated. Additionally, new results are presented on shallow furnace-annealed B junctions and shallow laser-annealed As junctions. Co-implanting B junctions with F is shown to degrade junction properties.

Silicon and selenium implantation and activation in In 0.53Ga 0.47As under low thermal budget conditions

Si and Se implantations have been systematically investigated in In 0.53Ga 0.47As. Different implant doses and various activation anneals with temperatures up to 700 °C have been examined. Raising Si implant dose from 1 × 10 14 to 1 × 10 15 cm −2 was found to increase the active doping concentration by about a factor of two. As confirmed by Transmission Electron Microscopy (TEM) and electrical measurements, the rest of the implanted Si ions remain as defects in the crystal and degrade the mobility. It was also confirmed from Secondary Ion Mass Spectrometry (SIMS) that the Si diffusivity in InGaAs is negligible up to 700 °C implant activation anneal making Si a suitable option for the formation of shallow junctions in InGaAs. The activation efficiency, sheet resistance, carrier density and mobility data of 25 keV Se and Si implanted InGaAs layers are also presented under various activation anneal temperatures.

Germanium $\hbox{n}^{+}/\hbox{p}$ Diodes: A Dilemma Between Shallow Junction Formation and Reverse Leakage Current Control

This paper shows that germanium n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> /p shallow junction formation often results in poor leakage current control. It is due to the counteraction between the fast diffusion of phosphorus and the high-temperature annealing requirement for dopant activation and defect annihilation. When the dopant concentration is above a threshold value, the concentration-dependent diffusion enhances phosphorus diffusion and results in a box profile, leading to an electrical concentration lower than its solid solubility limit. A refrained thermal budget may increase the active concentration, but it is not sufficient to repair the implantation-damaged lattice. Moreover, any plasma-involved fabrication processes after rapid thermal annealing may introduce additional field-assisted defects into the depletion region when the junction is near the surface. Thus, several tradeoffs must be considered between high P activation, low junction leakage, and a shallow junction in order to obtain functional negative-channel metal-insulator-semiconductor field-effect transistors.

On the diffusion and activation of ion-implanted n-type dopants in germanium

Some unresolved issues with respect to diffusion and activation of n-type ion-implanted dopants in germanium and of particular interest for shallow junction formation are pointed out and critically discussed. In particular, the absence of extrinsic diffusion during rapid thermal annealing at electron concentrations in the range of a few times 1019 cm−3 and the occurrence of a saturation dopant activation level of the order of 5×1019 cm−3 have been investigated more closely. It is shown that the former can be understood by considering a diffusivity enhancement factor (n/ni)2, with n the free electron concentration and ni the intrinsic carrier concentration, respectively. The saturation of the dopant activation, on the other hand, is determined by the density of states in a degenerately doped semiconductor. Based on these insights, some guidelines for controlling the excess n-type dopant diffusion and activation in germanium can be derived.

High temperature antimony ion implantation in strained silicon-on-insulator

We present experimental results on shallow junction formation in strained silicon-on-insulator by antimony ion implantation and standard rapid thermal processing. An attempt is made to obtain Sb activation without layer amorphization by implanting Sb at elevated temperature. The focus is on studying the Sb activation during implantation at high temperature. Rutherford backscattering spectrometry and secondary ion mass spectroscopy are employed for characterization of Sb diffusion in amorphous and crystalline Si. The results are discussed in terms of the defect reaction kinetics involved.