Yongjun Jeff Hu

Comparative Study of Self-Sputtering Effects of Different Boron-Based Low-Energy Doping Techniques

Angle-resolved X-ray photoelectron spectroscopy method was used to study self-sputtering effects of different p-type (boron-based) low-energy doping techniques, including conventional monoatomic 11B beam-line ion implant, molecular beam-line ion implants, cluster B beam-line ion implant, and plasma doping (PLAD). It has been found that the self-sputtering effects of the beam-line implants correlate with the mass of ion species except for BF2 implant. Cluster B implant shows severe self-sputtering effect and surface roughness due to its very heavy and very large cluster ions. BF2 implant shows severe sputtering/etching effect but comparable roughness due to a combination of the physical sputtering and reactive ion etching. PLAD processes using B2H6 and BF3 gas species have no sputtering effects but have deposition under certain process conditions.

Study of Low-Energy Doping Processes Using Continuous Anodic Oxidation Technique/Differential Hall Effect Measurements

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.

Study of Carrier Mobility of Low-Energy High-Dose Ion Implantations

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.

Direct Measurements of Self-Sputtering, Swelling, and Deposition Effects of N-Type Low-Energy Ion Implantations

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.

Doping Process for 3-D N-Type Trench Transistors-2-D Cross-Sectional Doping Profiling Study

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.

CMOS Device Performance Improvement Using Flood Buried-Contact Plasma Doping Processes

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 × 1016/cm2 dose regime beam-line B implants, were utilized for this process. The pMOS devices exhibit significant performance improvements, including ~80% lower contact resistances, similar threshold and subthreshold voltage characteristics, and ~15%-30% higher drive currents, without degrading OFF current. Using ULE BF3 PLAD, the nMOS devices also show performance improvements, including ~50% lower contact resistances, similar threshold and subthreshold voltage characteristics, and ~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.

Channeling effect and energy contamination evaluations of B-based beam-line ULE implants - Tools and recipe set-up dependence

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 (xj). 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 (xj) due to energy contamination as a secondary order effect.

High temperature Plasma Immersion Ion Implantation of AsH3 using PULSION

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.

Scalability study of boron-based ULE implants for advanced CMOS technology

Conventional beam-line (BL) implant shows a poor scalability of profiles (x_j) versus energy at the ULE implant regime due to serious channeling effect and energy contamination issue. B₂H₆ PLAD shows intrinsic channeling effect immunity with a totally different mechanism. An in-situ, build-in B deposition layer is formed during PLAD process as a screen amorphous layer to minimize channeling effect and reduce the surface damage residues as well. For above reasons, B₂H₆ PLAD shows a good scalability of profiles (x_j) versus energy, and achieves better R_S-x_j characteristics and x_j abruptness, and then better device performance including lower series and contact resistances, better I_ON/I_OFF ratio and less short channel effect (SCE), etc. than BL implant counterparts.

Plasma Chemistry Study of PLAD Processes

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.