G. H. Ma

The observation of trapping and detrapping effects in high-k gate dielectric MOSFETs by a new gate current Random Telegraph Noise (IG-RTN) approach

A new method, called gate current random telegraph noise (IG RTN), was developed to analyze the oxide quality and reliability of high-k gate dielectric MOSFETs. First, a single electron trapping/detrapping from process induced trap in nMOSFET was observed and the associated physical mechanism was proposed. Secondly, IG RTN has also been successfully applied to differentiate the difference in electron tunneling mechanism for a device under high-field or low-field stress. Finally, the soft-breakdown (SBD) behavior of a device can be clearly identified. Its IG RTN characteristic is different from that before soft-breakdown. It was found that SBD will indeed induce extra leakage current as a result of an additional breakdown path.

More strain and less stress- the guideline for developing high-end strained CMOS technologies with acceptable reliability

In this paper, the design guideline with emphasis on CMOS device reliability has been addressed. Advanced 65 nm CMOS devices with various strain engineering were evaluated. For nMOSFETs, charge pumping (CP) measurement is efficient for their reliability characterizations. Although biaxial strained SiGe-channel device provides good driving current enhancement, it suffers from the Ge out-diffusion such that exhibits worse reliability. The SSOI device exhibits good hot-carrier immunity, but its interface quality needs special care during the process. In addition, SiC on S/D device is an alternative for high current enhancement, but its off-state junction leakage is serious. Then, CESL device becomes the most promising technology with high performance and the best reliability, especially with process simplicity. For pMOSFETs, both uniaxial and biaxial strained devices have been studied. For the first time, an accurate representation of interface trap (Nit) profiling, suitable for HC and NBTI analyses, has been developed by an improved DCIV method. The uniaxial-strained device shows much better reliability, in particular a special class of SiGe S/D device with EDB design seems to be promising. These results provide a valuable guideline for the aggressive design of strained CMOS technologies.

New Observations on the Uniaxial and Biaxial Strain-Induced Hot Carrier and NBTI Reliabilities for 65nm Node CMOS Devices and Beyond

In this paper, new observations on the uniaxial and biaxial strain-induced hot carrier reliability and/or NBTI in nMOSFET and pMOSFET respectively have been reported for the first time. Uniaxial and biaxial strained nMOSFET and pMOSFET have been extensively examined. Different mechanisms are responsible for different strains in nMOSFET and pMOSFET. For the nMOFETs, it was found that uniaxial strain device has comparable HC reliability with the control device, while biaxial SiGe-strained device exhibits a much worse reliability. This is related to a large impact ionization rate in a biaxial strain which leads to a much worse reliability. For the pMOSFETs, either uniaxial or biaxial strained device shows a comparable amount of HC degradation, while SiGe S/D strained structure might be better considering process complexity, performance, and reliability. Although NBTI is still a great concern in SiGe S/D devices, embedded SiGe S/D technique can improve greatly the device NBTI reliability. These results provide a valuable guideline for the present 65nm and beyond CMOS device design with focus on the strain engineering.

Strain Effects of Si and SiGe Channel on (100) and (110) Si Surfaces for Advanced CMOS Applications

High performance SiGe channel CMOS on (100) and (110) Si surfaces with process-induced strained-Si technologies was fabricated and compared to Si channel devices. The mechanism of stress-induced performance enhancements in SiGe channel devices on both (100) and (110) surfaces was systematically investigated. Device-level piezoresistance coefficients for Si and SiGe channels were extracted from CMOS transistors with external mechanical stress applied. The results were consistent with device drive current enhancement induced by the CESL strained scheme.

Mobility and Strain Effects on /(110) SiGe channel pMOSFETs for High Current Enhancement

Mobility and strain mechanisms of SiGe channel pMOSFETs fabricated with <110> channel direction on (110) Si substrate (<110>/(110) SiGe channel) have been studied in details for the first time. The combination of substrate orientation, high mobility channel material and extrinsic stained-Si process demonstrates the ultra high mobility enhancement and results in 80% current gain. The piezoresistance coefficients of <110>/(110) SiGe channel p-MOSFETs were also studied to analyze the strain effect on current enhancement. We also compared the derived piezoresistance coefficients results of SiGe channel on (100) and (110) surfaces

The Channel Backscattering Characteristics of Sub-100nm CMOS Devices with Different Channel/Substrate Orientations

The channel backscattering and injection velocity of carriers in advanced CMOS devices are the two key parameters for achieving high drain current enhancement. For the first time, an extensive study of these transport parameters for different substrate orientations has been evaluated for both nMOSFET and pMOSFET. By suitably choosing the substrate orientation, it may achieve a reduced backscattering and an increased injection velocity, which is preferable for designing high performance logic CMOS devices. Results show that, in pMOSFET, (110) substrate is preferred and current enhancement can be greatly enhanced in the <112> channel. In comparison, (110) substrate in nMOSFET has an adverse effect in reducing driving current as a result of poorer transport characteristics. Therefore, (100) substrate is expected for nMOSFET design. A guideline is then summarized for the optimum design of high performance CMOS devices.

Improved Layout Dependence in High Performance SiGe Channel CMOSFETs

The device degradation problem due to compressive STI in devices with narrow width or small diffusion length can be greatly relieved in SiGe channel devices with the post-STI epitaxy process. The (110)SiGe PMOS realizes 77% current gain over (100)Si PMOS at 1um gate width, and current gain is increased to 112% at 0.12um gate width. A 42% current improvement in (100)SiGe NMOS at 0.12um gate width is also reported. Moreover, for diffusion length ranging from 2.71um to 0.26um, less than 4% current variation is obtained in SiGe channel devices compared to the 8~12% current variation in Si channel devices. The improved layout dependence is resulted from the lower STI stress in post-STI SiGe epitaxy process.

Technology Roadmaps on the Ballistic Transport in Straln Engineered Nanoscale CMO0S Devices

As device channel length continues to scale beyond 90nm, carrier transport in the ballistic regime becomes critically important. In this paper, the strain engineering and its correlation to the ION current enhancement of CMOS devices in the ballistic regime has been examined. It was characterized by two parameters, the ballistic transport efficiency and the injection velocity. Experimental verifications on very high mobility n- and p-MOSFET channel/substrate orientations with various strains have been made. For nMOSFETs, it shows that uniaxial tensile-stress using CESL is more efficient in current enhancement than the biaxial stress with bulk strained-SiGe technique. For the pMOSFETs, compressive stress using uniaxial or biaxial has been evaluated for various structures. It was found that both ballistic efficiency and the injection velocity can be enhanced in a specific pMOS structure with appropriate combination of CESL and biaxial strain. The technology roadmaps have then been established from advanced 65 nm CMOS devices. These results provide a guideline for designing high performance strained technology for CMOS devices in the sub-100 nm regime.

SiGe Channel CMOSFETs Fabricated on (110) Surfaces with TaC/HfO2 Gate Stacks

The promising potential of SiGe channel for next generation CMOSFETs applications has been demonstrated on (110) surfaces. SiGe channel CMOSFETs with TaC/FffO2 gate stack were fabricated on (110) surfaces for the first time. By introducing SiGe for channel material, the mobility of n/p-MOSFETs with TaC/HfO2 gate stacks can be greatly improved compared to Si channel devices with the same metal-gate/high-K gate stacks. The (110) SiGe channel n/p-MOSFETs with TaC/FffO2 gate stacks show 1.8x and 2.4x mobility enhancements over (110) Si devices with TaC/HfO2. The 23% propagation time delay improvement of ring oscillators fabricated with (110) SiGe channel CMOSFETs and poly/oxynitride gate stacks also proves the feasibility of (110) SiGe channel.

The understanding of strain-induced device degradation in advanced MOSFETs with process-induced strain technology of 65nm node and beyond

In this paper, the origin of the strained-induced degradation in the MOSFETs with process-induced strain has been investigated by the ID-RTN (Drain Current Random Telegraph Noise)technique. The process-induced strain on devices will make worse the device reliability, as reported in [1–2]. First, the ID-RTN has been employed to study the reliability of two different types of strain devices, i.e., the CESL strain and SiC S/D strain on nMOSFETs. Both CESL and SiC S/D nMOSFETs exhibit poorer reliability compared to bulk devices. However, their impacts to the much worse degradation are different. Results demonstrated that, for the strain in CESL device, it introduced extra mobility scattering in the vertical direction, while in SiC S/D device, the tensile strain along the channel causes an increase of trap generation via the horizontal field only. The CESL process introduces an additional compressive strain vertical to the channel such that it shows much worse reliability than the SiC S/D ones.