Shallow Junction Formation Research Articles

Small B-cluster ions induced damage in silicon

Small molecule-cluster ions, such as BF2, BSi, BGe, B10H14 and Bn can be used for shallow junction formation. We studied the cluster induced damage in silicon with different small clusters in keV energy range. The radiation damage was measured by glancing angle RBS/channeling. The measurement shows that the cluster induced damage per atom is quite different from the monomer ion induced damage at the same velocity. The small-cluster ions show strong enhanced radiation damage per atom. In this paper we will show non-linear effects on small boron-cluster induced damage in silicon. The cluster size dependence of this non-linear effect will also be presented.

Recent advances in R&D of gas cluster ion beam processes and equipment

This report reviews a new field of ion beam technology that employs accelerated ions consisting of clusters of a few hundreds to thousands of atoms (Gas Cluster Ion Beam technology, GCIB). Cluster ion-surface collisions have been found to produce low energy bombardment effects at very high density and GCIB processes exhibit unique non-linear effects that are useful for novel surface processing applications. The effects include low energy ion bombardment, lateral sputtering, and low temperature thin film formation. GCIB processing has been successfully applied for shallow junction formation; for high rate etching; for surface smoothing of materials including metals, dielectrics, superconductors and diamond; and for high-k oxide and DLC thin film deposition. Currently, industrial applications of GCIB processes are being conducted by several Japanese companies under the Nanotechnology program called “Advanced Nano-Fabrication Process Technology Using Quantum Beams” of NEDO/METI (New Energy and Industrial Technology Development Organization/the Ministry of economy and Technology Industry). In US, R&D especially for semiconductor applications are under way at Epion Corporation, International SEMATEC and their cooperated associations. Epion is the only company that is developing industrial GCIB equipment and has joined the NEDO/METI project.The review includes recent equipment and process developments. In nano-scale GCIB processes, the effect of cluster size (atoms/cluster) on surface processing, especially damage production, becomes important. In the project, GCIB equipment with cluster size selection system has been developed. Several industrial applications for surface smoothing of magnetic and semiconductor materials by the Japanese government and IC processing by US companies are summarized.

Optimization of advanced PMOS junctions using Ge, B and F co-implants

The main challenges for PMOS ultra shallow junction formation remain the transient enhanced diffusion (TED) and the solid solubility limit of boron in silicon. It has been demonstrated that low energy boron implantation and spike annealing are key in meeting the 90nm technology node ITRS requirements. To meet the 65nm technology requirements many studies have used fluorine co-implantation with boron and Si+ or Ge+ pre-amorphization (PAI) and spike annealing. Although using BF2+ can be attractive for its high throughput, self-amorphization and the presence of fluorine, many studies have shown that the fluorine successfully reduce TED, its energy needs to be well optimized with respect to the boron’s, therefore BF2+ does not present the right fluorine/boron energy ratio for the optimum junction formation. In this work we optimize the fluorine energy for boron energies down to 200eV. We show the dependence of optimized junction on Ge+ energies of 2keV and 20keV. We also demonstrate that the fluorine dose needs to be carefully optimized, otherwise a reverse effect can be observed.

Ultra shallow junction formation and dopant activation study of Ga implanted Si

The trend for decreasing geometries within CMOS architecture is driving the need for ever shallower, highly doped, low resistivity layers in silicon. The conventional dopant of choice, boron, as a result of its light mass requires that implant energies be ever reduced to meet the demands of these shallow junctions, with the inevitable effect on throughput due to implanter beam current limitations.In this paper we investigate using secondary ion mass spectrometry (SIMS), spreading resistance profiling (SRP) and Hall effect measurements, the alternate p-type dopant species of Ga and its behaviour in the energy range 2–5keV, implanted into both single crystal Si and pre-amorphised material.

Electrical characterization of 5 keV phosphorous implants in silicon

Si(100) wafers were implanted with 5-keV phosphorous (fluences of 1×1014–1×1016cm−2) and then annealed at 600–1000 °C, for 30 s or for 5 mins, to study shallow junction formation. Carrier densities were obtained by Van de Pauw Hall measurements, and carrier concentrations were depth profiled via a native-oxide stripping, differential Hall technique. For implanted fluences ⩾5×1014cm−2, an amorphous silicon surface layer is created. This results in solid-phase epitaxial growth at low annealing temperatures (600 °C), with reverse annealing upon dissolution of end-of-range interstitial clusters at higher temperatures (>700°C). Sheet resistances as low as 20Ω∕sq with electrical activation approaching 100% were achieved after annealing at 1000 °C.

Current research and development topics on gas cluster ion-beam processes

This report reviews the developing field of ion-beam technology that employs accelerated ions consisting of clusters of a few hundreds to thousands of atoms (gas cluster ion-beam technology, GCIB). Cluster ion-surface collisions have been found to produce low-energy bombardment effects at very high density, and GCIB processes exhibit unique nonlinear effects that are useful for surface processing applications. The effects include low-energy ion bombardment, lateral sputtering, and low-temperature thin-film formation. GCIB processing has been applied to shallow junction formation; high rate etching; surface smoothing of materials including metals, dielectrics, superconductors, and diamonds; and high-k oxide and diamond-like carbon thin-film deposition. We describe the unique characteristics of GCIB-surface interactions and GCIB process applications for (i) ultrashallow junction formation and doping in Si, (ii) surface smoothing of metals, (iii) selective smoothing of silicon-on-insulator SiC, and other compound semiconductor films, (iv) integrated circuit back-end-of-the-line processing, and (v) high-quality multilayer thin-film formation for reliable and durable optical filters.

Recovery of Silicon by Coherent Phonon Excited by Free Electron Laser Irradiation

One of the most important processes for ULSI devices is the formation of shallow junctions. Many technologies using laser processing have been developed to recover crystal defects and activate implanted ions in silicon. We propose a novel technology for recovery of crystal defects in silicon at low temperature in comparison with the conventional thermal process by using coherent lattice vibration with high energy, which is excited in the silicon due to absorption of mid-infrared light and multi phonon generation in the silicon substrate. In this paper, we report that the crystal defects which were introduced by the As ion implantation in the silicon substrate can be recovered by laser irradiation with wavelength of 16.4 pm using a Free Electron Laser (FEL). We also discuss how the recovery mechanism is absolutely different from the conventional thermal process by nanosecond laser irradiation or non-thermal process by femtosecond laser irradiation.

Laser thermal processing using an optical coating for ultra shallow junction formation

Semiconductor doping is a critical step in microelectronic device fabrication. Particularly, ultra-shallow junction formation for the CMOS 45-nm node is today intensively studied. Laser thermal processing (LTP) has already shown potentiality to achieve abrupt and ultra-shallow junctions, with a very low resistivity. However, the laser process has to be integrated in the conventional process flow of a real CMOS device fabrication. Therefore, the laser treatment needs to preserve the integrity of the different irradiated structures like transistor gates. Optical coatings, including reflective and anti-reflective coatings, can be used to protect the structures and to control the lateral diffusion of the dopants. In this work, we have studied different optical coatings (different materials and thicknesses) irradiated by a long pulse SOPRA VEL 15 excimer laser (200 ns–15 J). Junctions have been characterized by 4-point probe, in situ reflectivity, UV photometry and secondary ion mass spectroscopy. The efficiency and the integrity of the different coatings have been studied for different laser irradiation conditions in solid and molten phases. The results show that a proper optical coating optimizes the coupling of the deposited laser energy and is promising for improving the integration of the laser activation process of future CMOS junctions.

Using point defect engineering to reduce the effects of energy nonmonochromaticity of B ion beams on shallow junction formation

We have shown that energy contamination introduced by deceleration technology, for increasing the beam currents available for low energy boron implants, can affect fabricated junctions adversely. Energy contamination at a level of 0.1% can extend the profile of 0.5 keV B implants 10 nm deeper after a 1050 °C spike annealing. A highly monoenergetic beam with energy contamination less than 0.1% is required for submicron devices. Furthermore, we have used MeV implantation as a technique of point defect engineering (PDE) to control boron diffusion. PDE can reduce boron clustering and enhance boron activation. Diffusion of B in the tail region has been reduced significantly and the boron profile is much sharper. PDE lowers the critical requirement for beam purity. We conclude that shallower and sharper box-like boron junctions can be achieved by PDE with sub-keV B implants with highly monoenergetic beams.

Formation of Shallow Junctions by HCl-Based Si Etch Followed by Selective Epitaxy of B-Doped Si1 − xGex in RPCVD

Formation of shallow source/drain junctions by using HCl-based Si etch followed by selective deposition of in situ heavily B-doped SiGe in a reduced pressure chemical vapor deposition reactor is presented. The etching parameters were optimized to obtain a smooth surface prior to deposition of the SiGe layers. In the epitaxy process, SiGe layers with a resistivity of Ω cm were obtained by tuning the partial pressure of the B and Ge precursors. A problem with selectivity in the epitaxy step was encountered when combing the etch and growth processes, but a practical solution is presented. Integration issues such as loading effect, pile-up, and defect generation have also been investigated. © 2004 The Electrochemical Society. All rights reserved.

Concentration profiles of antimony-doped shallow layers in silicon

Antimony implants at 40 keV and at a dose of 4 × 1014 cm−2 have been characterized for their potential use in n-type shallow junction formation. The electrical characterization was done using sheet resistivity and Hall effect measurements. High electrical activities (>80%) and low sheet resistance values (<200 Ω/□) were obtained for annealing temperatures below 800 °C. A novel differential Hall effect technique was used to obtain doping profiles at a depth resolution down to 1 nm, with a comparison made between these and Rutherford backscattering (RBS) measurements of the atomic profile as a function of annealing temperature. The antimony shows insignificant diffusion for annealing temperatures of 800 °C and below, with junction depths of about 60 nm. Electrical activation correlates well with the substitutional fraction of antimony determined by RBS.

Formation of shallow junctions through BGe molecular ion implantation and rapid thermal annealing

This study investigated the implantation of BGe molecular ions into silicon together with post-annealing. The implantation ion energy and fluence were 77 keV and 5 × 10 14 cm −2, respectively. Secondary ion mass spectrometry (SIMS) results revealed that the effects of radiation-enhanced diffusion (RED) led to a deeper boron depth profile in the as-annealed specimen compared to the as-implanted one. The junction depths for a boron level of 10 17 cm −3 were 129 and 189 nm for the as-implanted and as-annealed specimens, respectively. Rutherford backscattering spectrometry with channeling (RBS/C) revealed an amorphous layer of approximately 70 nm in thickness in the as-implanted specimen, consistent with the cross-sectional transmission electron microscopy (XTEM) observations as well as SRIM simulations. Notably, amorphization was significantly reduced following rapid thermal annealing treatment, a finding confirmed in both the RBS/C and XTEM results. Plan-view transmission electron microscopy (PTEM) observations indicated no visible defects but only germanium precipitations with relatively sparse distribution.

Recent developments and applications of plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is an established technique in some niche microelectronics applications, such as synthesis of silicon on insulator. In other applications, such as shallow junction formation by plasma doping, trench doping, and others, PIII possesses unique advantages over conventional techniques. In the last few years, there have been significant breakthroughs in these areas. Recent developments in plasma doping, direct-current plasma immersion ion implantation that excels in planar sample processing, PIII of insulating materials, as well as plasma surface modification of biomaterials are reviewed in this article.

Optimization of Fluorine Co-implantation for PMOS Source and Drain Extension Formation for 65nm Technology Node

ABSTRACTThe main challenges for PMOS ultra shallow junction formation remain the transient enhanced diffusion (TED) and the solid solubility limit of boron in silicon. It has been demonstrated that low energy boron implantation and spike annealing are key in meeting the 90 nm technology node ITRS requirements. To meet the 65 nm technology requirements many studies have used fluorine co-implantation with boron and Si+ or Ge+ pre-amorphization (PAI) and spike annealing. Although using BF+2 can be attractive for its high throughput, self-amorphization and the presence of fluorine, many studies have shown that for the fluorine to successfully reduce TED its energy needs to be well optimized with respect to the boron's, therefore BF+2 does not present the right fluorine/boron energy ratio for the optimum junction formation. In this work we optimize the fluorine energy when a deep or shallow PAI is used. We also demonstrate that the fluorine dose needs to be carefully optimized otherwise a reverse effect can be observed. We will also show that the optimized junction depends less on the Ge+ energies between 2 keV and 20 keV and when HF etch is implemented after Ge+ PAI, improvements in both the junction depth and the sheet resistance are observed.

The Role of Preamorphization and Activation for Ultra Shallow Junction Formation on Strained Si Layers Grown on SiGe Buffer

In advanced CMOS technology nodes one may achieve further enhancement of device performance by carrier mobility modification in the transistor channel. The carrier mobility enhancement can be realized by formation of strained silicon layers on a Si1−xGex strain relaxed buffer. Formation of source and drain extensions on such structures need to satisfy one additional requirement, the formation process, including the activation related thermal budget should not relax the strain in the channel. In this paper we separately investigate the role of amorphization during implantation, different doping impurities and thermal budget on the junction and the transistor channel regions properties. Two approaches of dopant activation are discussed: low temperature solid phase epitaxial regrowth and high temperature conventional spike.

(A)thermal migration of Ge during junction formation in s-Si layers grown on thin SiGebuffer layers

ABSTRACTSolid phase epitaxial regrowth (SPER) has been proven to be highly advantageous for ultra shallow junction formation in advanced technologies. Application of SPER to strained Si/SiGe structures raises the concern that the Ge may out diffuse during the implantation and/or anneal steps and thus reduce the strain in the top silicon layer.In the present studies we expose 8-30 nm strained silicon layers grown on thin relaxed SiGe-buffers, to implant conditions and anneal cycles, characteristic for formation of the junctions by solid phase epitaxial regrowth and conventional spike activation. The resulting Geredistribution is measured using SIMS. Based on the outdiffused Ge-profiles the Ge-diffusion coefficient has been determined in the temperature range of 800-1100C from which an activation energy of ∼ 3.6 eV can be deduced. Up to 1050 C, 10 min, even a 30 nm strained film remains highly stable and shows only very moderate outdiffusion.We also have observed a far more efficient, athermal Ge-redistribution process linked to the implantation step itself. This was studied by analysing the Ge-redistribution following an Asimplant (2-15 keV, 5 1014 – 3 1015 at/cm2). It is shown that the energy of the implant species (or more specifically the position of the damage distribution function relative to the Ge-edge) plays a determining factor with respect to the Ge-migration. For implants whereby the damage distribution overlaps with the Ge-edge, a very efficient transport of the Ge is observed, even prior to any anneal cycle. The migration is entirely correlated with the collision cascade and the resulting (forward!) Ge-recoil distribution. The scaling with dose for a given energy links the observed Ge-profile with a broadening mechanism related to the number of atom displacements induced in the sample within the vicinity of the Si-SiGe-transition.

Randomization of heavily damaged regions in annealed low energy Ge +-implanted (0 0 1)Si

Apparent growth of amorphous layers during low temperature annealing was observed in low energy Ge +-implanted (0 0 1)Si by high-resolution transmission electron microscopy. The occurrence of abnormal growth is due to the randomization of heavily damaged regions beneath the original amorphous/crystalline interfaces. The randomization process is attributed to the strain, incurred by the presence of a high density of large Ge atoms in the heavily damaged Si substrate, relaxation to lower the free energy of the systems. The randomization upon annealing may be fruitfully applied to minimize the transient enhanced diffusion in shallow junction formation.

Boron cluster ions from source of negative ions by cesium sputtering

One of the ion implantation challenges for shallow junction formation is the production of high beam current at very low energy. Implantation of boron-containing clusters, such as B n , SiB n , GeB n and B 10H 14 is a potential solution for this problem. Due to the higher cluster ion energy for the lower partial energy of the boron atom, the space-charge limit to the transport of the boron-containing cluster ion beams can be reduced by a factor of M/ m, where M and m are the masses of the cluster and the boron atom, respectively. For a cluster of n boron atoms, the total gain in the cluster beam transport is n× M/ m. In this paper, we will present new data on the extraction of boron-containing clusters with a Source of Negative Ions by Cesium Sputtering. For some clusters, the ion beam current can be increased by 1 to 2 orders of magnitude by adjusting the source parameters. Our experience in the successful extraction of boron-containing clusters may be useful in the design of high current ion sources.

Semiconductor applications of plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is an established technique in certain niche microelectronics applications such as the synthesis of silicon-on-insulator. In other applications such as shallow junction formation by plasma doping, trench doping, and fabrication of blue light emitting materials, PIII has unique advantages over conventional techniques and may be the technique of choice in the future. There have been significant developments in these areas and recent breakthroughs in plasma and trench doping are discussed in this review paper. Results pertaining to direct-current PIII that excels in planar sample processing as well as the optical characteristics of nano-cavities produced by hydrogen PIII are also presented.

Laser thermal processing for ultra shallow junction formation: numerical simulation and comparison with experiments

In the last few years, laser thermal processing (LTP) has become a potential solution for sub-0.1 μm technology requirements, as focused by the international technology roadmap for semiconductors (ITRS). This paper presents a numerical simulation of the propagation of the melting front and regrowth of Si-based structures during excimer (XeCl-308 nm) laser irradiation. The influence of the pulse duration is highlighted in the simulation and compared with experiments. Two different types of XeCl lasers with different pulse durations have been used for the experiments in order to validate the model (SOPRA VEL 15, 200 ns, 15 J and Compex Lambda Physik, 20 ns, 200 mJ). The comparison between the simulation and the experimental results has been carried out using results from in situ reflectance measurements (transient reflectivity), secondary ion mass spectroscopy, spreading resistance profiles and four-point probes. The different implantation conditions used for this study were B + or BF 2 + implanted Si wafers, with or without Ge + pre-amorphization. Both experimental and simulation results show the potentiality of the LTP annealing technique for realization of ultra shallow junction under 0.1 μm.