Thermal laser stimulation
Encyclopedia
Thermal laser stimulation represents a class of defect imaging techniques which employ a laser
to produce a thermal variation in a semiconductor device
. This technique may be used for semiconductor failure analysis
. There are four techniques associated with thermal laser stimulation: optical beam induced resistance change (OBIRCH), thermally induced voltage alteration (TIVA)), external induced voltage alteration (XIVA) and Seebeck effect imaging (SEI)
line which is carrying a current
, the resulting resistance
changes can be detected by monitoring the input current to the device. OBIRCH is useful for detecting electromigration
effects resulting in open metal lines.
A constant voltage
is applied to the device-under-test (DUT). An area of interest is selected on the device, and a laser beam is used to scan the area. The input current being drawn by the device is monitored for changes during this process. When a change in current is noted, the position of the laser at the time that the change occurred is marked on the image of the device.
When the laser beam strikes a location which does not contain a void, good thermal transmission exists and the change in electrical resistance is small. In areas containing voids, however, thermal transmission is impeded, resulting in a larger change in resistance. The degree of resistance change is displayed visually on an image of the device, with areas of higher resistance being displayed as bright spots.
that the device uses.
A laser is scanned over the surface of the device while it is under electrical bias. The device is biased using a constant current source, and the power supply pin voltage is monitored for changes. When the laser strikes an area containing a short circuit, localized heating occurs. This heating changes the resistance
of the short, resulting in a change in power consumption of the device. These changes in power consumption are plotted onto an image of the device in locations corresponding to the position of the laser at the time that the change was detected.
is created. This would normally result in a change in current, however, the constant current choke prevents this from happening. The detection of these events allows the position of the defect to be determined.
. The thermal gradients induced generate corresponding electric potential
gradients. This correlation of thermal and electric gradients is known as the Seebeck effect. The SEI technique is used to locate electrically floating conductors.
When the laser changes the thermal gradient of a floating conductor, its electrical potential changes. This change in potential will change the bias of any transistors connected to the floating conductor, which affects the heat dissipation
of the device. These changes are mapped to a visual image of the device in order to physically locate the floating conductors.
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
to produce a thermal variation in a semiconductor device
Semiconductor device
Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices in most applications...
. This technique may be used for semiconductor failure analysis
Failure analysis
Failure analysis is the process of collecting and analyzing data to determine the cause of a failure. It is an important discipline in many branches of manufacturing industry, such as the electronics industry, where it is a vital tool used in the development of new products and for the improvement...
. There are four techniques associated with thermal laser stimulation: optical beam induced resistance change (OBIRCH), thermally induced voltage alteration (TIVA)), external induced voltage alteration (XIVA) and Seebeck effect imaging (SEI)
Optical beam induced resistance change
Optical beam induced resistance change (OBIRCH) is an imaging technique which uses a laser beam to induce a thermal change in the device. Laser stimulation highlights differences in thermal characteristics between areas containing defects and areas which are defect-free. As the laser locally heats a defective area on a metalMetal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
line which is carrying a current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
, the resulting resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
changes can be detected by monitoring the input current to the device. OBIRCH is useful for detecting electromigration
Electromigration
Electromigration is the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. The effect is important in applications where high direct current densities are used, such as in...
effects resulting in open metal lines.
A constant voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
is applied to the device-under-test (DUT). An area of interest is selected on the device, and a laser beam is used to scan the area. The input current being drawn by the device is monitored for changes during this process. When a change in current is noted, the position of the laser at the time that the change occurred is marked on the image of the device.
When the laser beam strikes a location which does not contain a void, good thermal transmission exists and the change in electrical resistance is small. In areas containing voids, however, thermal transmission is impeded, resulting in a larger change in resistance. The degree of resistance change is displayed visually on an image of the device, with areas of higher resistance being displayed as bright spots.
Thermally induced voltage alteration
Thermally induced voltage alteration (TIVA) is an imaging technique which uses a laser beam to pinpoint the location of electrical shorts on a device. The laser induces local thermal gradients in the device, which result in changes to the amount of powerPower (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
that the device uses.
A laser is scanned over the surface of the device while it is under electrical bias. The device is biased using a constant current source, and the power supply pin voltage is monitored for changes. When the laser strikes an area containing a short circuit, localized heating occurs. This heating changes the resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
of the short, resulting in a change in power consumption of the device. These changes in power consumption are plotted onto an image of the device in locations corresponding to the position of the laser at the time that the change was detected.
External induced voltage alteration
External induced voltage alteration (XIVA) maintains a constant voltage bias and constant current sensing on the device under test. When the scanning laser passes over a defective location, a sudden change in impedanceElectrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
is created. This would normally result in a change in current, however, the constant current choke prevents this from happening. The detection of these events allows the position of the defect to be determined.
Seebeck effect imaging
Seebeck effect imaging (SEI) uses a laser to generate thermal gradients in conductorsElectrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
. The thermal gradients induced generate corresponding electric potential
Electric potential
In classical electromagnetism, the electric potential at a point within a defined space is equal to the electric potential energy at that location divided by the charge there...
gradients. This correlation of thermal and electric gradients is known as the Seebeck effect. The SEI technique is used to locate electrically floating conductors.
When the laser changes the thermal gradient of a floating conductor, its electrical potential changes. This change in potential will change the bias of any transistors connected to the floating conductor, which affects the heat dissipation
Thermal management of electronic devices and systems
Heat generated by electronic devices and circuitry must be dissipated to improve reliability and prevent premature failure. Techniques for heat dissipation can include heatsinks and fans for air cooling, and other forms of computer cooling such as liquid cooling....
of the device. These changes are mapped to a visual image of the device in order to physically locate the floating conductors.