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An additional ultrashallow boron-based plasma doping (PLAD) was carried out into the source/drain contacts for both pMOS and nMOS devices without masks. The PLAD using either B2H6 or BF3 gas in a mild energy to ultralow energy (ULE) regime, which are roughly equivalent to 1.5–0.2-keV energy and 1–3 $\times 10^{16}$ /cm $^{2}$ dose regime beam-line B implants, were utilized for this process. The pMOS devices exhibit significant performance improvements, including $\sim 80$ % lower contact resistances, similar threshold and subthreshold voltage characteristics, and $\sim 15$ %–30% higher drive currents, without degrading OFF current. Using ULE BF3 PLAD, the nMOS devices also show performance improvements, including $\sim 50$ % lower contact resistances, similar threshold and subthreshold voltage characteristics, and $\sim 4$ % higher drive currents without degrading OFF current. The mechanism of the nMOS device performance improvement can be attributed to the Schottky barrier height lowering effect and deactivation improvement. It significantly reduces cost because this one low-cost PLAD module eliminates two photo steps, one implant step, and two photo removing/cleaning steps.

As transistor technologies continue to scale and device density increases, junction formation requirements are subject to increasing challenges. Ion implantation is the preferred approach for junction formation due to its precise control of dopant depth and dose. These aspects are crucial to deliver finely tuned transistor performance and limit device variation. Arsenic and phosphorus (n-type) dopants are used at many process steps to dope crystalline silicon, polycrystalline silicon, or other substrates in advanced memory devices. Arsenic, due to its heavy mass, will readily amorphize crystalline silicon, particularly at high dose rates. Conventional thermal processing is used to recover crystalline silicon amorphization, but may be subject to residual defects. Heating the substrate during implantation is a novel technique, which has been adopted in advanced semiconductor devices to limit the amorphous region and allow for complete recrystallization in subsequent thermal processes [1]. This work demonstrates wafer-level results of heating the substrate in a plasma doping (PLAD) tool.

Comparison study of doping a 3-D trench transistor structure is carried out by beam-line (BL) implant and plasma doping (PLAD) methods. Electron holography (EH) is used as a powerful characterization method to study 2-D cross-sectional doping profiles of arsenic-based doping processes. Quantitative definitions of junction depths xj in both vertical and lateral directions can be obtained. Good correlations of 2-D EH dopant profiles, 1-D secondary ion mass spectrometry/angle-resolved X-ray electron spectroscopy impurity profiles, and device electrical parameters are demonstrated. The results reveal an advantage of PLAD over BL implant: a much larger effective implant area for 3-D trench bottom. It leads to a deeper vertical junction depth xj(V) with a larger lateral junction depth xj(L). It is due to the PLAD technology with less angle variation issues and no line of sight shadowing effect. Enhancing the dopant lateral straggle by PLAD at the trench bottom is particularly useful for nonplanar device structures with low resistance buried dopant layers.

SiF4 PLAD has been systematically characterized and optimized. The correlations between the etching, deposition, retained F dose and profile as functions of the PLAD process variables including implant voltage, RF power, pressure, pulse duty cycle, and the diluting gases have been extensively investigated. It was found that PLAD process by using pure SiF4 is in an etching or RIE regime, but can be adjusted to minimize the etching effect. It was found that diluting SiF4 with different gases can significantly impact etching and deposition characteristics. The selectivity of etching and deposition behaviors on the different substrate materials such as poly-Si, silicon oxide, and silicon nitride have been explored. With the understanding of these behaviors, SiF4 PLAD can be optimized for multiple precision doping and material modification applications.

The continuous anodic oxidation technique/differential Hall effect technique is used to study damage engineering of ultralow energy doping. It has been found that the scattering defect concentrations of the beam-line (BL) implants strongly correlate to the implant ion specie atomic mass unit and energy. Plasma doping (PLAD) seems to show a different mechanism for scatter defects. PLAD processes can have an in situ B-deposited film during implant and have less direct ion bombardment on the Si surface. The low scattering defect concentrations of PLAD implants (B2H6 and BF3) indicate that PLAD implants show an intrinsic advantage over BL counterparts in the current process regime.

New carrier drift mobility data for boron-, phosphorus-, and arsenic-doped Si in a low-energy high-dose implant regime are measured and studied using a continuous anodic oxidation technique/differential Hall effect technique. The data show that, when the doping concentration is >; 1020/cm3, both the hole and electron mobility values are lower than the conventional model predictions, and the electron mobility of the As-doped Si is lower than that of the P-doped ones. The data also show that, when the doping concentration is >; 1021/cm3 the hole mobility in the B-doped Si and the electron mobility in the P-doped Si are almost equal and reach as low as ~40 cm2/V · s, and the electron mobility of the As-doped Si is the lowest and reaches ~30 cm2/V · s. These mobility data are much lower than the conventional model predictions and are also lower than the previously published data. For the ULSI device and circuit analyses, simulations, and designs, these new mobility data need to be taken into consideration.

Combination of transmission electron microscopy and secondary ion mass spectrometry methods and device characteristics are used to successfully study damage engineering of the B-based low energy ion implants. The depths and densities of the amorphizing (a-Si) layer (surface lattice damage) and the end of range (EOR) damage are found to correlate to ion mass (amu) and implant energy, which are scalable to the molecular ion implants and ultralow energy) implants. The B11 beam-line implant shows thinner both a-Si and EOR depths due to its smaller amu and lower energy, and the damage are well annealed under the current annealing conditions. The BF2 beam-line implant shows severe surface lattice damage by more amorphizing due to its larger amu and higher energy, and needs more thermal budget to annealing (recrystallizing). The B2H6 plasma doping (PLAD) shows moderate a-Si layer and less EOR damage than beam-line ones which attributes to B deposition as a screen so that there are no direct ion bombardments on S...

Angle-resolved X-ray photoelectron spectroscopy method was used to study self-sputtering effects of different n-type low-energy doping techniques, including conventional monoatomic 75As and 31P beam-line ion implants and AsH3 plasma doping (PLAD). It has been found that the self-sputtering effects of the beam-line implants correlate with the mass of ion species. As beam-line implant shows more serious self-sputtering effect than monoatomic P and B beam-line implants. Very low energy P implants show surface-swelling phenomena. PLAD process using AsH3 gas species has no sputtering effects but has slight deposition under current process condition.

Comparing with conventional spreading resistance profiling and differential Hall effect (DHE) methods, the continuous anodic oxidation technique/DHE (CAOT/DHE) technique may achieve more reasonable profiles of carrier concentration nh(x), mobility muh(x), and resistivity rho(x) and more reasonable carrier dose and xj in Si substrate. It has been successfully used to study ultralow energy doping techniques including B beam-line implant and B2H6 plasma doping (PLAD). CAOT/DHE data support the fact that the devices fabricated by PLAD achieve improvement to those fabricated by beam-line implant because PLAD offered higher surface carrier concentration and carrier dose. CAOT/DHE data quantitatively verify the so-called solid solubility limit activation theory - the carrier profiles and secondary ion mass spectrometry (SIMS) B impurity profiles under BSS are very well consistent on both beam-line and PLAD implants. As a cheaper and standard metrology, the SIMS/ARXPS method with the solid solubility limit activation theory may be used to quantitatively or semiquantitatively study the doping and activation processes.

A newly developed surface analysis technique, which combines secondary ion mass spectrometry with angle-resolved X-ray photoelectron spectroscopy, was used to achieve more accurate results of the retained impurity doses and profiles for ultralow-energy implants, including conventional beamline implant and plasma immersion ion implantation (PIII). Using this method, it has been found that the B2H6 (diborane) PIII demonstrates thicker native oxide and much more B dose loss during rapid thermal processing and surface-cleaning treatments than conventional beamline ion implantation, due to the higher surface B concentration. In order to match the electrical parameters of the device, PIII must consider higher nominal dose to compensate the B loss.

A new method and apparatus called Faraday/ion mass spectroscopy (IMS) dosimeter system is developed and can be used to determine the implanted impurity dose and profile for any molecular or multispecies-based plasma immersion ion implantation (PIII)/plasma doping (PLAD) processes. Good agreement between the boron doses measured by this method and those measured by SIMS has been demonstrated. Because of its direct, real-time, in situ, and close-loop control manner, this method shows a good controllability and repeatability for the PIII/PLAD processes.

It has been shown that plasma immersion ion implantation (PIII)/plasma doping (PLAD) processing offers unique advantages over conventional beam-line ion implant systems, including system simplicity, lower cost, higher throughput, and device performance improvements. A 78-nm channel length PMOS device, which is fabricated by a B2H6/H2 PIII/PLAD process on source/drain doping, can offer better device performance that includes a 50% lower contact resistance (RCS), 11%-16% higher drive current (IDS), and transconductance (KL) than those fabricated by beam-line implantation. The physical mechanisms behind the device performance improvement can be correlated to the much lower RCS, which in turn results from the unique dopant profiles of the PIII/PLAD process.

The P+ plasma doping (PLAD) process using B 2 H 6 /H 2 plasma in a pulsed, RF-excited plasma system has been systematically characterized and optimized. The correlations between the deposition, retained B dose/profile, carrier dose/profile, sheet resistance ( R S ) as a function of the pulse voltage, nominal dose, and carrier gas dilution have been extensively investigated. It was found that diluting B 2 H 6 with H 2 can be used as a method to control and minimize boron deposition. SIMS and SRP analyses indicate that B and carrier profiles are deeper for higher dilutions up to 5/95 of a B 2 H 6 /H 2 gas ratio, than they are for lower dilutions due to less B deposition. This results in a higher activation fraction because of the B SS limit and compensates for the reduction of the retained B dose. The higher dilutions also improved the retained B dose and R S saturation due to less deposition. The PLAD process of a pulsed, RF-excited plasma system using B 2 H 6 diluted with 92.5% to 95% H 2 was found to be an optimal condition for high-dose, boron-doping applications.

We extensively investigate tool and recipe set-up dependence of the ultra-shallow junctions (USJ) doped by the boron-based ultra-low energy (ULE) beam-line (BL) implants. Recipes set-up includes different tools, energies, implant temperatures, and deceleration ratios. Channeling effect and energy contamination issues are de-coupled by drift and deceleration mode implants. A channeling effect factor (CEF) is defined and quantified. Channeling effect is found to be a major factor causing deeper profiles and long tails (x j ). Channeling effect gets worse when the implant energy is reduced due to less self-PAI effect (with less damage). Low temperature (−100 °C) implant does not effectively reduce channeling effect. Deceleration mode implant increases tail (x j ) due to energy contamination as a secondary order effect.

Plasma immersion ion implantation (PIII) technology is an alternative that overcomes the limitations of conventional beam line ion implantation for shallow, high dose and 3D doping on advanced memory and logic devices. This technique also delivers a better CoO as the result of higher productivity, smaller footprint and lower operating costs. With the requirements of new device architecture such as FINFET or FD-SOI for Logic, reduction of cell sizes for Memories, or 3D integration for “More than Moore” applications, a shallow profile is not the only critical objective. Amorphization and defects prevention become key points to allow good recrystallization and activation after annealing while reducing the thermal budget. IBS has developed and implemented the technique of high temperature implantation (up to 500°C) on the PIII system, PULSION®. In this paper, we present the impact of high temperature AsH3 Plasma doping in silicon. ARXPS (Angle Resolution X-ray Photoelectron Spectroscopy), SIMS (Secondary Ion Mass Spectrometry), and TEM (Transmission Electron Microscopy) analysis are used to study impact of the temperature on doping profiles and amorphization layer thickness. We show that when “high” acceleration voltage and high doses are used, thickness of the amorphization layer is drastically reduced (figure 1), and when lower acceleration voltage is used, amorphization layer can be totally suppressed.

An ultra-low energy high dose B-based implant was processed after source and drain region formed and before metal sillicide contact formed for PMOS devices. B beam-line (BL) implant and plasma doping (PLAD) using either B 2 H 6 or BF 3 gases were utilized for this process. PMOS device performance showed significant improvements, including ∼70 percent lower contact resistances, similar threshold and sub-threshold characteristics, and ∼15 percent higher drive currents without degrading off current. PLAD is preferred on this application because of its much higher throughput in this process regime.

PLAD (plasma doping) is promising for both evolutionary and revolutionary doping options because of its unique advantages which can overcome or minimize many of the issues of the beam-line (BL) based implants. In this talk, we present developments of PLAD on both planar and 3D device structures. Comparing with the conventional BL implants, PLAD shows not only a significant production enhancement, but also a significant device performance improvement and 3D structure doping capability, including an 80% contact resistance reduction, more than 25% drive current increase, and conformal doping on non-planar device structures. In PLAD developments and applications, the conventional metrologies are not suitable for PLAD process because of their limits and PLAD's unique properties. Novel diagnostic metrologies for PLAD process have been developed and are also presented in this talk.

Comparison study of doping a 3D trench transistor structure was carried out by beam-line (BL) implant and plasma doping (PLAD) methods. Electron holography (EH) was used as a powerful characterization method to study 2D cross-sectional doping profiles of boron-based doping processes. Quantitative definitions of junction depths xj in both vertical and lateral directions can be obtained. Good correlations of 2D electron holography dopant profiles, 2D dopant profile simulations, and 1D SIMS/ARXPS impurity profiles are demonstrated. The results reveal an advantage of PLAD over BL implant: a much larger effective implant area for 3D trench bottom. It leads to a larger lateral junction depth xj(L) with a comparable vertical junction depth xj(V). It is attributed to the PLAD technology with no line of sight shadowing effect and less angle variation issues. Enhancing the dopant lateral straggle by PLAD at the trench bottom is particularly useful for non-planar device structures with low resistance buried dopant layers.

Plasma doping (PLAD) shows very different impurity profiles compared to the conventional beam-line-based ion implantations due to its non-mass separation property and plasma environment. There is no simulation for PLAD process so far due to a lack of a dopant profile model. Several factors determine impurity profiles of PLAD process. The most significant factors are: plasma chemistry and deposition/etching characteristics of multi-ion species plasmas. In this paper, we present plasma chemistry and deposition/etching characteristics of PLAD processes versus co-gas dilutions. Four dopant plasmas including B2H6, BF3, AsH3, and PH3, and two non-dopant plasmas including CH4 and GeH4 are studied and demonstrated.

Plasma doping (PLAD) has been adopted across the implant technology space and into high volume production for both conventional DRAM and NAND doping applications. PLAD has established itself as an alternative to traditional ion implantation by beamline implantation. The push for high doping concentration, shallow doping depth, and conformal doping capability expand the need for a PLAD solution to meet such requirements. The unique doping profile and doping characteristics at high dose rates allow for PLAD to deliver a high throughput, differentiated solution to meet the demand of evolving transistor technology. In the PLAD process, ions are accelerated to the wafer as with a negative wafer bias applied to the wafer. Competing mechanisms, such as deposition, sputtering, and etching inherent in plasma doping require unique control and process optimization. In this work, we look at the distinctive process tool control and characterization features which enable an optimized doping process using n-type (PH3 or...

The effects of self-amorphization thickness on boron (B) dopant depth profile in silicon (Si) were investigated by cold temperature implant, down to −100°C. Significant B junction depth (Xj) reduction can be achieved for as-implant and post anneal, when the self-amorphization thickness is comparable or deeper than the B implant projected range (implant peak position) and the implant is completed at sufficiently low temperature. There is a transition temperature regime before the appropriate temperature is reached. The Xj reduction is stagnated due to the thickness limitation and the degree of self-amorphization. Temperature dependent surface damage, self-amorphization thickness, diffusion, and activation were also studied. Improvement in carrier mobility is more significant in certain dose regimes at low temperatures. The findings of this study provide important insight in to the control of the junction profile for smaller atomic mass unit (AMU) species, like B, by using the self-amorphization effect at cold temperatures.

High vacuum scanning spreading resistance microscopy (HV‐SSRM) and electron holography (EH) methods are used to study two‐dimensional (2D) cross‐sectional doping profiles of low energy high dose ion implantations including conventional beam‐line 75As implant and AsH3 plasma doping (PLAD). Both methods show quantitative definition of junction depths xj in vertical and lateral directions, and have been demonstrated to be powerful techniques for 2D doping profiling study. It has been found that AsH3 PLAD with −10 kV voltage and 1×1016/cm2 dose shows slightly deeper junction depth xj, both of vertical xj(V) and lateral xj(L) and with slightly larger xj(L)/xj(V) ratio than beam‐line 75As implant with 10 keV energy and 8×1015/cm2 dose. Good correlations among 2D HV‐SSRM doping profiles, 2D EH doping profiles, 2D doping profile simulation, and 1D SIMS/ARXPS As profiles have been demonstrated. Very good correlation between 2D doping profiles and device parameters has been demonstrated.

The focus of this paper is a comparative study of the advanced boron-based ultra-low energy (ULE) doping techniques on ultra-shallow junction (USJ) fabrications, including beam-line atomic 11B implant, BF 2 , B 18 H 22 , C 2 B 10 H 12 molecular implants, cluster B implant, and B 2 H 6 and BF 3 PLAD implants. It has been found that B 2 H 6 PLAD and B 18 H 22 molecular implants demonstrate the best R S -x j and abruptness characteristics. Beam-line BF 2 implant shows poor R S -x j characteristics due to its serious RIE effect by F species. Cluster B implant shows the worst R S -x j characteristics and a very rough surface. Both are attributed to its serious self-sputtering effect because of its much larger and heavier ion species although further optimization may lead to improvement.

New carrier mobility (μ) data for boron-, phosphorus-, and arsenic-doped Si in a low-energy, high-dose implant regime are measured and studied using continuous anodic oxidation technique/differential Hall effect (CAOT/DHE) technique. The data show that when the doping concentration is >1020/cm3, both hole and electron mobility values are lower than the conventional model predictions, and the electron mobility of the As-doped Si is lower than the P-doped ones. The data also show that when the doping concentration is >1021/cm3, the hole mobility in B-doped Si and the electron mobility in P-doped Si are almost equal and reach as low as ~40 cm2/V sec, and the electron mobility of As-doped Si is the lowest and reaches ~30 cm2/V sec. These mobility data are much lower than the conventional model predictions and are also lower than the previously published data. For the ULSI device and circuit analyses, simulations, and designs, these new mobility data need to be taken into consideration.

The plasma doping technique offers unique advantages over conventional beam line systems, including system simplification, lower cost, higher throughput, and device performance equivalence or improvement. Plasma doping has been first used on 68 nm CMOS device source and drain formations. A PMOS device was doped by B2H5 plasma doping and an NMOS device was doped by AsH3 plasma doping. The devices fabricated by plasma doping processes were intensively evaluated in this paper. In addition to higher throughput, CMOS devices, both PMOS and NMOS devices, fabricated by plasma doping processes showed improved electrical performance to those fabricated by conventional beam line ion implantation, including ~10-20 percent lower contact resistances, similar threshold and sub-threshold characteristics, ~10 percent higher drive currents and transconductances, and better device performance curves.

The differential Hall effect CAOT permits rapid accurate measurement of mobility, resistivity, and carrier concentration. For single crystal structures with carrier concentrations less than 1E20 B cm−3 the resistivity‐carrier concentration tracks the A.S.T.M. F‐723 algorithm relationship. Above ∼1E20 B cm−3, a scattering defect mobility component is added to the phononic and coulombic components. This component is significantly greater for beamline implantation than for plasma doping for both single crystal junctions and polysilicon films.

A newly‐developed surface analysis technique, which combines Secondary Ion Mass Spectrometry (SIMS) with Angle‐Resolved X‐ray Photoelectron Spectroscopy (ARXPS), was used to achieve more accurate results of the retained impurity doses and profiles for ultra‐low energy implants, including conventional beam‐line implant and plasma immersion ion implantation (PIII). Using this method, it has been found that the B2H6 (Diborane) PIII demonstrates thicker native oxide and much more B dose loss during RTP and surface clean treatments than conventional beam‐line ion implantation, due to the higher surface B concentration. In order to match the electrical parameters of the device, PIII must consider higher nominal dose to compensate the B loss.

It has been shown that the PIII/PLAD poly-Si gate doping process offers unique advantages over conventional beam line systems, including system simplification, lower cost, higher throughput, and device performance equivalence or improvement. PMOS devices fabricated by a B 2 H 6 /H 2 PIII/PLAD process on P+poly-gate doping are intensively evaluated in this paper. In addition to higher throughput, PMOS devices fabricated by a PLAD process showed an equivalent electrical performance to those fabricated by conventional beam line ion implantation, including similar poly-Si gate resistance and depletion, threshold and sub-threshold characteristics, drive current, and gate-oxide integrity.

An ambient-controlled scanning spreading resistance microscopy (AC-SSRM) apparatus is utilized for one-dimensional (1D) and two-dimensional doping profiling measurement. 1D SSRM profiling on a blanket (vertical) B-doped Si wafer is conducted to obtain a spreading resistance profile SR(x). Modeling is used to convert SR(x) to carrier profile n(x). Replacing the average mobility (μ) with a calibration using μ(x), the carrier (hole) profile n(x) is more accurate. This is especially pronounced near the surface and junction depth (xj) and is consistent with the continuous anodic oxidation technique/differential Hall effect (CAOT/DHE) measured carrier profiles. The model based on AC-SSRM data obtained xj = 103.4 nm, which was consistent to secondary ion mass spectrometry results of xj = 104.0 nm. Calibrated hole dose using μ(x) is 9.6 × 1014/cm2 and is relatively closer to DHE hole dose 1.4 × 1015/cm2. In addition, a fairly good consistency of sheet resistance (RS) values among 4 point probe (4PP), CAOT/DHE, an...

The impacts of the native oxides and the impurity loss mechanisms of low energy doping process for both p-type and n-type implants have been quantitatively studied using secondary ion mass spectrometry/angle-resolved x-ray photoelectron spectroscopy method. The low energy doping processes include conventional beamline implant and plasma immersion ion implantation (PIII). It has been found that the native oxides play very significant roles on the low energy implants, especially for PIII due to its unique impurity profiles. The results show very different behaviors on p-type and n-type implants because of the SiO2∕Si interface segregation mechanisms. p-type (boron-based) doping loses more impurities into the native oxide, but n-type (arsenic-based) doping does not lose impurities. These results can be used to optimize the semiconductor processes such as implant, strip, clean, and thermal-annealing process.

Several metrologies may be used to analyze plasma doping (PLAD) [S. Qin and A. McTeer, IEEE Trans. Electron Devices 54, 2497 (2007)] results, each with its own advantages and disadvantages. An investigation into the available characterization methods has been performed in order to reduce costs associated with the current qualification process, such as additional clean and annealing steps. This article will introduce an improved analytical method developed at Micron and demonstrate results of a correlation study between characterization techniques for B doped PLAD. The combined secondary ion mass spectrometry/angle-resolved x-ray electron spectroscopy two-dimensional (2D) dose mapping data provide excellent confirmation of the low energy x-ray emission spectroscopy (LEXES) 2D dose mapping data, and the nonuniformity from annealing can be deconvoluted from nonuniformities due to the implantation process. The data demonstrate that LEXES may replace the thermally processed RS measurement for tool and/or proce...

Johnsen–Rahbek type (JR type) electrostatic chuck (ESC) was found to be more sensitive to wafer conditions than classic ESC, including backside dielectric quality and thickness, wafer type, and doping level. Wafer type and doping level may significantly affect the reliability of ESC operations, depending on ESC configurations and operation conditions. Deep-depletion breakdown phenomenon of a JR type ESC operation, which is equivalent to a metal-insulator-semiconductor capacitor, was simulated by PISCES-IIB device simulator, and it was found to be a mechanism of the reliability and pop-off issues of JR type ESC operations. In this paper, the potential solutions are proposed to solve these issues.

A Johnsen–Rahbek (J-R type) type electrostatic chuck (ESC) was found to be more sensitive to wafer conditions than classic ESC, including backside dielectric quality and thickness and doping level. The wafer backside dielectric may reduce the clamp force and increase the declamping time, depending on dielectric quality, dielectric thickness, and ESC configurations. These issues and their mechanisms are studied extensively and potential solutions are proposed.

It has been reported that helium dilution of B2H6 in the plasma doping (PLAD) process can be used to control and minimize deposition phenomenon. In this article we quantify the impact of such dilution on boron doping and deposition under PLAD conditions appropriate for ultrashallow junction formation. The sheet resistance (RS) of the implanted wafers remains nearly constant when B2H6 is diluted with He up to 95%, although the retained B dose is reduced. Secondary ion mass spectroscopy profiles indicate that B profiles are deeper for higher dilution than for lower dilution due to less B deposition. The deeper B profiles contribute to a higher activation fraction during annealing due to the B solid solubility limit. This higher activation compensates for the reduction of the retained B dose. The plasma doping process of a pulsed glow-discharge system by using B2H6 diluted with 95% provides optimal conditions for minimizing deposition. This results in a higher doping rate and then higher throughput.