Y. Jeff Hu

PLAD (Plasma Doping) on 22nm Technology Node and Beyond - Evolutionary and/or Revolutionary

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 PLADs unique properties. Novel diagnostic metrologies for PLAD process have been developed and are also presented in this talk.

Co-gas impact of B2H6 plasma diluted with helium on the plasma doping process in a pulsed glow-discharge system

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.

Ambient-controlled scanning spreading resistance microscopy measurement and modeling

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...

Damage engineering of boron-based low energy ion implantations on ultrashallow junction fabrications

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...

Characterization of hot N-type plasma doping (PLAD) implantation

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.

Characteristics of SiF4 Plasma Doping (PLAD)

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.

LDD implant process optimization for high voltage NMOS improvement

In this paper, we demonstrate that high voltage NMOS is very sensitive to LDD implant process conditions. With the same implant energy and dose, high voltage NMOS channel punch through BVDSS tail is strongly toggled by critical implant process parameters such as beam current and beam size. Lower beam current density reduces both implant damage and beam angular divergence. As a result, LDD lateral junction tail under the channel is shortened and the variation of the channel punch-through is reduced. However, lower beam current degrades the throughput and increases the cost of the implant. On the other hand, longer effective channel length reduces HV NMOS sensitivity to LDD implant beam current and enables higher beam current implant without BVDSS tail, but there is trade-off on other device performance and it is limited by design rules. From device point of view, lower beam current implant is often chosen as the final solution with the price for higher implant cost. This study is very important for us to understand that when we optimize the implant process setup, we should not only consider about throughput improvement by pushing up higher beam current, but also closely watch device sensitivity to different implant process setup.

Trench doping process for 3D transistors - 2D cross-sectional doping profiling study

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 l...

Two‐Dimensional Cross‐Sectional Doping Profile Study of Low Energy High Dose Ion Implantations Using High Vacuum Scanning Spreading Resistance Microscopy (HV‐SSRM) and Electron Holography

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.

Study of Carrier Mobility of Low-Energy, High-Dose Ion Implantations Using Continuous Anodic Oxidation Technique/Differential Hall Effect (CAOT/DHE) Measurements

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.