Time-dependent gate oxide breakdown

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Time-dependent gate oxide breakdown (or time-dependent dielectric breakdown, TDDB) is a failure mechanism in MOSFETs, when the gate oxide breaks down as a result of long-time application of relatively low electric field (as opposed to immediate breakdown, which is caused by strong electric field). The breakdown is caused by formation of a conducting path through the gate oxide to substrate due to electron tunneling current, when MOSFETs are operated close to or beyond their specified operating voltages.

The gate oxide is the dielectric layer that separates the gate terminal of a MOSFET from the underlying source and drain terminals as well as the conductive channel that connects source and drain when the transistor is turned on. Gate oxide is formed by thermal oxidation of the silicon of the channel to form a thin insulating layer of silicon dioxide. The insulating silicon dioxide layer is formed through a process of self-limiting oxidation, which is described by the Deal Grove model. A conductive gate material is subsequently deposited over the gate oxide to form the transistor. The gate oxide serves as the dielectric layer so that the gate can sustain as high as 1 to 5 MV/cm transverse electric field in order to strongly modulate the conductance of the channel.

Wafer (electronics) thin slice of semiconductor material used in the fabrication of integrated circuits

In electronics, a wafer is a thin slice of semiconductor, such as a crystalline silicon (c-Si), used for the fabrication of integrated circuits and, in photovoltaics, to manufacture solar cells. The wafer serves as the substrate for microelectronic devices built in and upon the wafer. It undergoes many microfabrication processes, such as doping, ion implantation, etching, thin-film deposition of various materials, and photolithographic patterning. Finally, the individual microcircuits are separated by wafer dicing and packaged as an integrated circuit.

Quantum tunnelling or tunneling is the quantum mechanical phenomenon where a subatomic particle passes through a potential barrier. Quantum tunneling is not predicted by the laws of classical mechanics where surmounting a potential barrier requires enough potential energy.

Contents

Models

The defect generation in the dielectric is a stochastic process. There are two modes of breakdown, intrinsic and extrinsic. Intrinsic breakdown is caused by electrical stress induced defect generation. Extrinsic breakdown is caused by defects induced by the manufacturing process. For Integrated circuits, the time to breakdown is dependent on the thickness of the dielectric (gate oxide) and also on the material type, which is dependent on the manufacturing process node. Older generation products with gate oxide thickness > 4nm are based on SiO2 and the advanced process nodes with gate oxide < 4nm are based on high-k dielectric materials. There are different breakdown models and thickness of the gate oxide determines the validity of the model. E model, 1/E model and power law exponential model are common models which depict the breakdown behavior.

Stochastic process mathematical object usually defined as a collection of random variables

In probability theory and related fields, a stochastic or random process is a mathematical object usually defined as a family of random variables. Historically, the random variables were associated with or indexed by a set of numbers, usually viewed as points in time, giving the interpretation of a stochastic process representing numerical values of some system randomly changing over time, such as the growth of a bacterial population, an electrical current fluctuating due to thermal noise, or the movement of a gas molecule. Stochastic processes are widely used as mathematical models of systems and phenomena that appear to vary in a random manner. They have applications in many disciplines including sciences such as biology, chemistry, ecology, neuroscience, and physics as well as technology and engineering fields such as image processing, signal processing, information theory, computer science, cryptography and telecommunications. Furthermore, seemingly random changes in financial markets have motivated the extensive use of stochastic processes in finance.

Semiconductor device fabrication process used to create the integrated circuits that are present in everyday electrical and electronic devices

Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications.

The term high-κ dielectric refers to a material with a high dielectric constant κ. High-κ dielectrics are used in semiconductor manufacturing processes where they are usually used to replace a silicon dioxide gate dielectric or another dielectric layer of a device. The implementation of high-κ gate dielectrics is one of several strategies developed to allow further miniaturization of microelectronic components, colloquially referred to as extending Moore's Law.

The failure types for integrated circuit (IC) components follow the classic bath tub curve. There is infant mortality, which is decreasing failure rate typically due to manufacturing defects. A low constant failure rate which is random in nature. Wear out failures are increasing failures due to aging semiconductor degradation mechanisms. TDDB is one of the intrinsic wear out failure mechanisms. Performance of the IC components can be evaluated for semiconductor wear out mechanisms including TDDB for any given operating conditions. The breakdown models mentioned above could be used to predict the time to fail for the component due to time dependent dielectric breakdown (TDDB).

Bathtub curve

The bathtub curve is widely used in reliability engineering. It describes a particular form of the hazard function which comprises three parts:

Test method

The most commonly used test for the investigation of TDDB behavior is "constant stress". [1] Constant stress tests can be applied in form of constant voltage stress (CVS) or constant current stress. In the former, a voltage (that is often lower than the breakdown voltage of the oxide) is applied to the gate, while its leakage current is being monitored. The time it will take for the oxide to break under this constant applied voltage is called the time-to-failure. The test is then repeated several times to obtain a distribution of time-to-failure. [1] These distributions are used to create reliability plots and to predict the TDDB behavior of oxide at other voltages.

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MOSFET transistor used for amplifying or switching electronic signals

The metal–oxide–semiconductor field-effect transistor is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, whose voltage determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. A metal-insulator-semiconductor field-effect transistor or MISFET is a term almost synonymous with MOSFET. Another synonym is IGFET for insulated-gate field-effect transistor.

CMOS technology for constructing integrated circuits

Complementary metal–oxide–semiconductor (CMOS) is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits. CMOS technology is also used for several analog circuits such as image sensors, data converters, and highly integrated transceivers for many types of communication. Frank Wanlass invented CMOS in 1963 while at Fairchild Semiconductor and was granted US patent 3,356,858 in 1967. In this groundbreaking patent, the fabrication of CMOS devices was outlined, on the basis of thermal oxidation of a silicon substrate to yield a layer of silicon dioxide located between the drain contact and the source contact.

Insulated-gate bipolar transistor three-terminal power semiconductor device

An insulated-gate bipolar transistor (IGBT) is a three-terminal power semiconductor device primarily used as an electronic switch which, as it was developed, came to combine high efficiency and fast switching. It consists of four alternating layers (P-N-P-N) that are controlled by a metal-oxide-semiconductor (MOS) gate structure without regenerative action. Although the structure of the IGBT is topologically the same as a thyristor with a 'MOS' gate, the thyristor action is completely suppressed and only the transistor action is permitted in the entire device operation range. It is used in switching power supplies in high power applications: variable-frequency drives (VFDs), electric cars, trains, variable speed refrigerators, lamp ballasts, and air-conditioners.

QBD is the term applied to the charge-to-breakdown measurement of a semiconductor device. It is a standard destructive test method used to determine the quality of gate oxides in MOS devices. It is equal to the total accumulated charge passing through the dielectric layer just before failure. Thus QBD is a measure of time-dependent gate oxide breakdown. As a measure of oxide quality, QBD can also be a useful predictor of product reliability under specified electrical stress conditions.

Threshold voltage Minimum source-to-gate voltage for a field effect transistor to be conducting from source to drain

The threshold voltage, commonly abbreviated as Vth, of a field-effect transistor (FET) is the minimum gate-to-source voltage VGS (th) that is needed to create a conducting path between the source and drain terminals. It is an important scaling factor to maintain power efficiency.

Power MOSFET power MOS field-effect transistor

A power MOSFET is a specific type of metal oxide semiconductor field-effect transistor (MOSFET) designed to handle significant power levels.

Transistors are simple devices with complicated behavior. In order to ensure the reliable operation of circuits employing transistors, it is necessary to scientifically model the physical phenomena observed in their operation using transistor models. There exists a variety of different models that range in complexity and in purpose. Transistor models divide into two major groups: models for device design and models for circuit design.

Capacitance–voltage profiling is a technique for characterizing semiconductor materials and devices. The applied voltage is varied, and the capacitance is measured and plotted as a function of voltage. The technique uses a metal–semiconductor junction or a p–n junction or a MOSFET to create a depletion region, a region which is empty of conducting electrons and holes, but may contain ionized donors and electrically active defects or traps. The depletion region with its ionized charges inside behaves like a capacitor. By varying the voltage applied to the junction it is possible to vary the depletion width. The dependence of the depletion width upon the applied voltage provides information on the semiconductor's internal characteristics, such as its doping profile and electrically active defect densities., Measurements may be done at DC, or using both DC and a small-signal AC signal, or using a large-signal transient voltage.

Charge Trap Flash (CTF) is a semiconductor memory technology used in creating non-volatile NOR and NAND flash memory. The technology differs from the more conventional floating-gate MOSFET technology in that it uses a silicon nitride film to store electrons rather than the doped polycrystalline silicon typical of a floating gate structure. This approach allows memory manufacturers to reduce manufacturing costs five ways:

  1. Fewer process steps are required to form a charge storage node
  2. Smaller process geometries can be used
  3. Multiple bits can be stored on a single flash memory cell.
  4. Improved reliability
  5. Higher yield since the charge trap is less susceptible to point defects in the tunnel oxide layer

Negative-bias temperature instability (NBTI) is a key reliability issue in MOSFETs. NBTI manifests as an increase in the threshold voltage and consequent decrease in drain current and transconductance of a MOSFET. The degradation is often approximated by a power-law dependence on time. It is of immediate concern in p-channel MOS devices (pMOS), since they almost always operate with negative gate-to-source voltage; however, the very same mechanism also affects nMOS transistors when biased in the accumulation regime, i.e. with a negative bias applied to the gate.

Hot carrier injection (HCI) is a phenomenon in solid-state electronic devices where an electron or a “hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term "hot" refers to the effective temperature used to model carrier density, not to the overall temperature of the device. Since the charge carriers can become trapped in the gate dielectric of a MOS transistor, the switching characteristics of the transistor can be permanently changed. Hot-carrier injection is one of the mechanisms that adversely affects the reliability of semiconductors of solid-state devices.

TDDB is an initialism that may refer to:

Tantalum capacitor

A tantalum electrolytic capacitor is an electrolytic capacitor, a passive component of electronic circuits. It consists of a pellet of tantalum metal as an anode, covered by an insulating oxide layer that forms the dielectric, surrounded by liquid or solid electrolyte as a cathode. Because of its very thin and relatively high permittivity dielectric layer, the tantalum capacitor distinguishes itself from other conventional and electrolytic capacitors in having high capacitance per volume and lower weight.

In electronics, leakage is the gradual transfer of electrical energy across a boundary normally viewed as insulating, such as the spontaneous discharge of a charged capacitor, magnetic coupling of a transformer with other components, or flow of current across a transistor in the "off" state or a reverse-polarized diode.

Failure of electronic components Ways electronic elements fail and prevention measures

Electronic components have a wide range of failure modes. These can be classified in various ways, such as by time or cause. Failures can be caused by excess temperature, excess current or voltage, ionizing radiation, mechanical shock, stress or impact, and many other causes. In semiconductor devices, problems in the device package may cause failures due to contamination, mechanical stress of the device, or open or short circuits.

In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, density is an intrinsic property of any physical object, whereas weight is an extrinsic property that depends on another object.

Physics of failure is a technique under the practice of Design for Reliability that leverages the knowledge and understanding of the processes and mechanisms that induce failure to predict reliability and improve product performance.

Electronic personal dosimeter

The electronic personal dosimeter (EPD) is a modern electronic dosimeter for estimating uptake of ionising radiation dose of the individual wearing it for radiation protection purposes. The electronic personal dosimeter has the advantages over older types that it has a number of sophisticated functions, such as continuous monitoring which allows alarm warnings at preset levels and live readout of dose accumulated. It can be reset to zero after use, and most models allow near field electronic communications for automatic reading and resetting.

References

  1. 1 2 Elhami Khorasani, Arash; Griswold, Mark; Alford, T. L. (2014). "A Fast $I{-}V$ Screening Measurement for TDDB Assessment of Ultra-Thick Inter-Metal Dielectrics". IEEE Electron Device Letters. 35 (1): 117–119. doi:10.1109/LED.2013.2290538. ISSN   0741-3106.
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