Non-melt Laser Annealing Research Articles

Effect of number of laser pulses on p+/n silicon ultra-shallow junction formation during non-melt ultra-violet laser thermal annealing

We investigate the effect of the number of laser pulses on the formation of p+/n silicon ultra-shallow junctions during non-melt ultra-violet laser (wavelength, 355nm) annealing. Through surface peak temperature calculating by COMSOL Multiphysics, the non-melt laser thermal annealing is performed under the energy density of 130mJ/cm2. We demonstrate that increasing the number of laser pulses without additional pre-annealing is an effective annealing method for achieving good electrical properties and shallow junction depth by analyzing sheet resistance and junction depth profiles. The optimal number of laser pulses is eight for achieving a high degree of activation of dopant without further increase of junction depth. We have also explained the improved electrical characteristics of the samples on the basis of fully recovered crystallinity as revealed by Raman spectroscopy. Thus, it is suggested that controlling the number of laser pulses with moderate energy density is a promising laser annealing method without additional pre-annealing.

Highly strained channel with low-resistivity carbon-doped source/drain formed by cascade C7Hx implantation followed by rapid solid-phase epitaxy and laser annealing for n-channel metal–oxide–semiconductor field-effect transistor

We show the systematical investigation results of the effects of the implanted ion dose of P or As under various solid-phase epitaxy (SPE) conditions on the local stress in channel regions in metal–oxide–semiconductor field-effect transistor (MOSFET) structures, and on sheet resistance and strain in carbon-doped source/drain (Si:C-S/D) layers. P or As substitution is in conflict with C substitution in Si:C layers during SPE. Furthermore, the amount of P incorporated instead of C into the Si lattice site is larger than that of As incorporated instead of C. Therefore, low-resistivity Si:C layers with low stress in the case of using P and high-resistivity Si:C layers with high stress in the case of using As are formed by single-step C7Hx implantation with rapid thermal annealing and nonmelt laser annealing, respectively. As a countermeasure, we demonstrate that cascade C7Hx implantation to control the C profiles in Si:C layers is effective for achieving high-strain channels and low-resistivity Si:C-S/D layers. Control of C profiles is a key technology for state-of-the-art complementary MOS devices with Si:C-S/D.

Effect of Pulse Number on Dopant Activation in Silicon during Shallow p+/n Junction Formation by Non-Melt Excimer Laser Annealing

Shallow p+/njunctions were formed using Ge-PAI and low-energy/high-dose boron-ion implantation, followed by thermal annealing involving nanosecondnon-melt excimer laser annealingandrapidthermal annealing. The effect of laser pulse number on dopant activation and regrowth of a-Si layer are discussed.We found that laser annealing aloneis insufficient to regrow a-Si layer and activate dopant. In contrast, activationwas observed in the samples that were subjected to preannealingrapid thermal annealing followed by non-melt laser annealing; with slight increase of sheet resistance valuewhen the number of laser pulse shot was increased. This is considered due to the interaction of dopant and supersaturated defect in the remaining a-Si layer.The percentage of defect-dopant interaction increased with the pulse shot numbers which contributed to the decrease in activation level.

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.

Formation of Ultra Shallow p+/n Junction in Silicon Using a Combination of Low-Temperature Solid Phase Epitaxy and Non-Melt Double-Pulsed Green Laser Annealing

MOSFETs scaling-down is an effective way to attain high-performance CMOS operating with lower power and leakage current. However, short channel effects have become a serious problem due to the shortening of channel length. One of the promising methods to suppress this problem is by forming a shallow, highly doped and activated source/drain extension region. Fabricating ultra shallow p+/n junction is difficult due to the channeling of boron ions and anomalous boron diffusion during fabrication processes. A combination of Ge pre-amorphization implantation, low-energy boron implantation and two-step annealing, involving low-temperature solid phase epitaxy preannealing followed by non-melt laser annealing was used for forming ultra shallow p+/n junction in silicon. The physical relationship among the regrowth of implanted layer, boron activation and diffusion, and leakage current is investigated. We have succeeded in forming ultra shallow p+/n junction with junction depth of 8 nm and sheet resistance of 920 Ω/□.

Comparison of Boron Diffusion in Silicon during the Formation of Shallow p+/n Junction with KrF and Green Laser Annealing

A combination of Ge pre-amorphization implantation (Ge-PAI), low-energy B implantation and non-melt laser annealing is a promising method to form highly-activated, abrupt and ultra-shallow junctions (USJ). In this work, shallow p+/n junction was formed by annealing the implanted sample with two different laser sources, i.e. by using excimer laser, KrF (λ= 248nm, pulse duration : 37ns) and green laser (λ= 527nm, pulse duration : 110ns) in order to compare the diffusion of boron during the formation of shallow p+/n junction. Experimental results show that remarkable boron diffusion occurred during annealing of the samples subjected to KrF laser annealing with a very short annealing time. Meanwhile, boron diffusion is controlled in the samples subjected to green laser annealing. We considered that the penetration depth and the pulse duration are the important factor that may caused the difference in boron diffusion during annealing process.

Alternating Reversed Scanning Sequence for Improved Within-Wafer Uniformity During Nonmelt Laser Annealing of Arsenic-Implanted Silicon

Beyond the 45-nm technology node, nonmelt laser thermal annealing (LTA) is a potential candidate to replace the spike rapid thermal annealing (RTA) for the formation of ultrashallow and highly activated source/drain extension junctions. However, one major drawback of LTA is that it is ineffective in the removal of implantation-induced damage. As such, arsenic deactivation, as a result of cluster formation due to the release of excess interstitials from the end-of-range (EOR) region, is observed when a post-LTA thermal budget is applied. Since conventional LTA comprises localized heating using a laser beam scanning the wafer front-side in a nonalternating sequence, different portions of the wafer will experience varying post-LTA thermal budget from the hotplate, depending on when the laser beam scans through it. Because dopant deactivation increases as the post-LTA thermal budget increases, severe degradation of the within-wafer uniformity is observed. To address this problem, a multiple-pulse, alternating reversed laser scanning technique is implemented to average out the differences in post-LTA thermal budget across the wafer between each pulse. Using such a scheme, the variations in subsequent dopant deactivation across the wafer is reduced and significant uniformity improvement of up to 50% is observed.

Carbon Incorporation into Substitutional Silicon Site by Molecular Carbon Ion Implantation and Recrystallization Annealing as Stress Technique in n-Metal–Oxide–Semiconductor Field-Effect Transistor

Since the lattice constant of silicon-carbon (Si:C) is smaller than that of Si, Si:C embedded in the source and drain (e-Si:C S/D) can induce tensile stress in the channel and improve the electron mobility of n-metal–oxide–semiconductor field-effect transistor (nMOSFETs). In this research, molecular carbon (C) ion implantation and recrystallization schemes employed to achieve strained Si:C films with a high substitutionally incorporated carbon concentration ([C]sub) and a high ratio of substitution were studied. Several recrystallization techniques including rapid-thermal-annealing (RTA)-based solid phase epitaxy (SPE), spike annealing, and nonmelt laser annealing have been used to optimize C incorporation into Si and strain application. Results of these different implantation and annealing techniques are compared and discussed. Furthermore, we proposed the first recrystallization by nonmelt laser annealing and the co-incorporation of a dopant that increases the rate of Si regrowth and has a covalent radius slightly different from that of Si. These processes markedly promoted the recrystallization of C densely incorporated in an amorphous Si layer and improved the crystallinity of strained Si:C films while maintaining a high [C]sub at a high ratio of substitution.

Deactivation Induced Within Wafer Nonuniformity During Nonmelt Laser Annealing of Arsenic and Phosphorus Implanted Silicon

In the setup for nonmelt laser spike anneal (LSA), the wafer is mounted with the front-side facing the laser beam and backside facing the heated hotplate. When arsenic or phosphorus-implanted silicon is subjected to LSA, sheet resistance degradation, indicative of dopant deactivation, is observed when the post-LSA thermal budget provided by the heated chuck (hotplate) is increased. This additional thermal budget is associated with the chuck temperature and duration a wafer is left on the chuck after LSA. The deactivation is believed to occur due to the ineffective removal of implantation damage by LSA, giving rise to the release of point defects during the post-LSA thermal cycle that aids inactive clusters formation. The observed phenomena severely degrades the within wafer uniformity since LSA is a localized heating process that relies on scanning the laser beam across the whole wafer. As such, different portions of the implanted silicon wafer will remain on the hotplate for varying durations depending on when the laser beam scans through a particular spot. By adopting a dual step source/drain anneal scheme that incorporates a spike rapid thermal annealing condition sufficient to anneal out the implantation damage prior to LSA, the within wafer nonuniformity issue can be rectified.

Non-melt laser annealing of Plasma Implanted Boron for ultra shallow junctions in Silicon

In this work we present results on sub-melt Excimer laser annealing in order to obtain difussionless activation of Boron for the creation of ultra shallow P-MOS devices. For the fulfillment of the strict requirements imposed by the ITRS roadmap for the 32 nm node we have implemented two emerging techniques: non-melt laser annealing and BF 3 Plasma Doping implantation (PLAD). By using PLAD, we were able to create ultra shallow and abrupt as implanted profiles. On the other hand, by performing laser annealing on the samples in the sub-melt regime, we can achieve high levels of electrical activation, while practically eliminating Boron diffusion, due to its capability to deliver low thermal budget in the sub-microsecond time scale. An Excimer KrF laser ( λ = 248 nm and pulse duration 38 ns) has been used. The post annealing characterization of the samples included SIMS and Van Der Pauw Sheet resistance measurements. SIMS data indicate almost difussionless dopant behavior with R s values at 680 Ω/sq. We have concluded our analysis with the examination of the morphological characteristics both of the surface of the sample using Atomic Force Microscopy (AFM) and the evolution of the recrystallization of the amorphized layers and the removal of the defects by means of cross-section Transmission Electron Microscopy.

Suppression of boron deactivation and diffusion in preamorphized silicon after nonmelt laser annealing by carbon co-implantation

For preamorphized boron-implanted samples subjected to nonmelt laser spike annealing (LSA), increasing the LSA temperature at temperatures below 1250 °C results in negligible sheet resistance changes due to the formation of inactive boron-interstitial clusters (BICs). These clusters, which are evidenced as a kink in the boron profile beyond the amorphous/crystalline interface, result chiefly from the inadequate removal of end-of-range (EOR) defects. When the LSA temperature is elevated beyond 1250 °C, sheet resistance improvement takes place due to the increase in active boron dose from the dissolution of the BIC at higher temperatures. Cluster dissolution also gives rise to a supersaturation of silicon interstitials that deepen the junctions as a result of transient enhanced diffusion (TED). With an additional post-LSA treatment, severe deactivation, especially at lower LSA temperatures, and further TED is observed. Two concurrent mechanisms, namely, boron clustering (which gives rise to deactivation and sheet resistance degradation) and dissolution of the BIC (which gives rise to TED) formed during the LSA step, are believed to take place during the post-LSA thermal budget. As the LSA temperature increases, TED from the as-LSA profile upon rapid thermal annealing (RTA) is significantly reduced as a result of the improved effectiveness of the EOR defect dissolution during the higher temperature LSA step. When carbon co-implantation is performed, deactivation and TED is successfully suppressed with the reduction in free silicon interstitial concentration due to the formation of complexes of carbon and silicon interstitials. The amount of deactivation upon RTA becomes independent of LSA temperature for the carbon-implanted samples, largely because boron clustering becomes limited by the small concentration of free silicon interstitials present instead of the LSA temperatures used.

Surface proximity and boron concentration effects on end-of-range defect formation during nonmelt laser annealing

The effects of surface proximity and B concentration on end-of-range defect formation during nonmelt laser annealing in preamorphized silicon have been studied. These effects were analyzed by observing the activation and diffusion of an ultrashallow B implant, using Hall effect and secondary ion mass spectrometry measurements. By adjusting the preamorphizing implant and laser annealing conditions, B deactivation and diffusion were minimized, resulting in a sheet resistance of ∼600Ω∕sq with a 16nm junction depth. This is attributed to a combination of enhanced dissolution of end-of-range defects and preferential formation of B-interstitial clusters due to the surface proximity and high B concentration, respectively.

Deactivation of ultrashallow boron implants in preamorphized silicon after nonmelt laser annealing with multiple scans

Electrical activation and redistribution of 500eV boron implants in preamorphized silicon after nonmelt laser annealing at 1150°C and isochronal rapid thermal postannealing are reported. Under the thermal conditions used for a nonmelt laser at 1150°C, a substantial residue of end-of-range defects remained after one laser scan but these were mainly dissolved within ten scans. The authors find dramatic boron deactivation and transient enhanced diffusion after postannealing the one-scan samples, but very little in the five- and ten-scan samples. The results show that end-of-range defect removal during nonmelt laser annealing is an achievable method for the stabilization of highly activated boron profiles in preamorphized silicon.

Enhanced Boron Activation in Strained-Si/Si1-xGex Substrate Using Laser Annealing

Strained-Si/SiGe substrate comprises a thermally less conductive SiGe layer, which deprives a good thermal dissipation pathway. This gives rise to a highly non- equilibrium laser process and can vary significantly to that in normal bulk silicon substrate. Our results show that the boron distribution in strained-Si/SiGe substrate is always deeper and more abrupt than that in bulk silicon substrate, signifying a substantial thermal confinement that leads to a greater melt extent and melting duration. It is found that a decrease of over 94% thermal transfer rate occurs in the strained-Si/SiGe substrate. Non-melt laser annealing, on the other hand, produces dopant profiles of negligible diffusion and improves activation in the strained-Si/SiGe substrates. No degradation in the strain in the strained-Si layer was induced after non- melt laser annealing. The study demonstrates that non-melt laser annealing in thermally less conductive semiconductor substrates is capable of enhancing dopant activation at low laser fluence.

Deactivation of Ultra Shallow B and BF2 Profiles After Non-melt Laser Annealing

AbstractUltra-shallow B and BF2 implants in silicon pre-amorphised with Ge have been activated using a scanning non-melt laser. The implants were activated either by using 1 or 10 laser scans. Isochronal 60s post-laser annealing between 700-1000°C were then undertaken to study the deactivation and reactivation of the B. Both B and BF2 samples were implanted with a dose of 1x1015 B cm-2 at an effective energy of 500eV. The presence of F from the BF2 implants, which is superimposed over the boron profile increases the sheet resistance of the initial fabricated junction (from 600-700 Ω/sq from B implants only to 750-1100 Ω/sq for BF2 implants). Fluorine also changes the deactivation and reactivation behaviour of the boron during the post-anneals by increasing the amount of deactivation of the boron.

Effect of Varying Dwell Time During Non-melt Laser Annealing of Boron Implanted Silicon

AbstractAs the fabrication for the CMOS technology trends to decreasing the size of transistors for the benefit of increased performance and device density, the implant and annealing process technologies are being forced to meet increasingly challenging demands for ultra-shallow junctions. As the current annealing preferences shift from rapid thermal annealing toward sub-second RTP technologies such as flash and laser annealing, the dynamics of micro-structural evolution on the order of milliseconds and microseconds become of increasing importance. To investigate the kinetics in this ultra-fast annealing regime, this study investigated the effect of varying the temperature and time of a scanning laser anneal in the millisecond and microsecond timeframe. Amorphous layers were created in silicon substrates using a 30 keV silicon implant at a dose of 1x1015 ions/cm3. These wafers were then processed using a scanning continuous wave near infra-red laser at varying temperatures and scan rates in order to vary the dwell time of each condition. A combination of sheet resistance, optical interferometry, and secondary ion mass spectrometry characterization techniques were used in order to investigate the activation and diffusion of these laser annealed samples. The regrowth temperature across all samples showed a positive correlation to the sheet resistance; trending toward lower values as temperatures increased. Dwell time, however, showed an inverse effect at lower temperatures. The microsecond anneal at 1200 °C showed a lower Rs than the millisecond anneal, while at higher temperatures the trend reversed. This trending shows an obvious competition between activation and diffusion mechanisms and their dependence on regrowth temperature.

Modeling and Experiments of Boron Diffusion During Sub-Millisecond Non-Melt Laser Annealing in Silicon

AbstractBoron diffusion and defect evolution during sub-millisecond (ms) laser annealing with partial SPER are investigated using secondary ion mass spectrometry and transmission electron microscopy. Boron diffusivity enhancement in amorphous-Si is observed during partial SPER at 550 °C. It is shown that boron diffusion during the laser annealing process is a 2-step diffusion (SPER + Laser). The depth of the amorphous layer affects the dopant activation behavior. During sub-ms laser annealing, end-of-range defects are formed and show an evolution behavior. {311} defects cannot completely transfer to dislocation loops after 1300 °C laser annealing. It is considered that the thermal budget of sub-ms laser is too small for full defect evolution. Atomistic diffusion modeling using a kinetic Monte Carlo method can explain the defect behavior during laser annealing.

Investigation of pulsed non-melt laser annealing on the film properties and performance of Cu(In,Ga)Se2 solar cells

Abstract Pulsed non-melt laser annealing (NLA) has been used for the first time to modify near-surface defects and related junction properties in Cu(In,Ga)Se2 (CIGS) solar cells. CIGS films deposited on Mo/glass substrates were annealed using a 25 ns pulsed 248 nm laser beam at selected laser energy density in the range 20–60 mJ/cm2 and pulse number in the range 5–20 pulses. XRD peak narrowing and SEM surface feature size increase suggest near-surface structure changes. Dual-beam optical modulation (DBOM) and Hall-effect measurements indicate NLA treatment increases the effective carrier lifetime and mobility along with the sheet resistance. In addition, several annealed CdS/CIGS films processed by NLA were fabricated into solar cells and characterized by photo- and dark-J–V and quantum efficiency (QE) measurements. The results show significant improvement in the overall cell performance when compared to unannealed cells. The results suggest that an optimal NLA energy density and pulse number for a 25 ns pulse width are approximately 30 mJ/cm2 and 5 pulses, respectively. The NLA results reveal that overall cell efficiency of a cell processed from an unannealed film increased from 7.69% to 13.41% and 12.22% after annealing 2 different samples at the best condition prior to device processing.

Nonmelt laser annealing of 5-KeV and 1-KeV boron-implanted silicon

Nonmelt laser annealing has been investigated for the formation of ultrashallow, heavily doped regions. With the correct lasing and implant conditions, the process can be used to form ultrashallow, heavily doped junctions in boron-implanted silicon. Laser energy in the nonmelt regime has been supplied to the silicon surface at a ramp rate greater than 10/sup 10//spl deg/C/s. This rapid ramp rate will help decrease dopant diffusion while supplying enough energy to the surface to produce dopant activation. High-dose, nonamorphizing boron implants at a dose of 10/sup 15/ ions/cm/sup 2/ and energies of 5 KeV and 1 KeV are annealed with a 308-nm excimer laser. Subsequent rapid thermal anneals are used to study the effect of laser annealing as a pretreatment. SIMS, sheet resistance and mobility data have been measured for all annealing and implant conditions. For the 5-KeV implants, the 308-nm nonmelt laser preanneal results in increased diffusion. However, for the 1-KeV implant processed with ten laser pulses, the SIMS profile shows that no measurable diffusion has occurred, yet a sheet resistance of 420 /spl Omega//sq was produced.