Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-06-19
2002-06-18
Nguyen, Vinh P. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S765010
Reexamination Certificate
active
06407560
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to failure analysis and qualification testing of integrated circuits (ICs) or microelectromechanical (MEM) devices, and specifically to an apparatus and method for analyzing an IC or MEM device for any open-circuit or short-circuit defects therein based on localized heating of electrical conductors or electrically-active members therein using a focused and scanned laser beam.
BACKGROUND OF THE INVENTION
Open-circuit and short-circuit defects in electrical conductors or electrically-active members in ICs or MEM devices can result in major yield and reliability problems. A capability for localizing and identifying these types of defects is important for analyzing ICs or MEM devices to determine failure mechanisms therein, for qualifying the ICs or MEM devices as known-good devices, and for implementing corrective action during fabrication to minimize the occurrence of such defects. Efficient and reliable detection for open-circuit and short-circuit defects will become of increasing importance as the number of interconnection levels and the length of interconnections increase with the development of new generations of ICs and MEM devices having on-board integrated circuitry. Efficient and reliable detection of short-circuit defects is also important for MEM devices where short-circuiting of electrically-active members can occur as a result of fabrication defects or stiction (i.e. adhesion of one or more electrically-active members with an adjacent electrically-active member or with a supporting substrate whereon the MEM device is formed.) Stiction in MEM devices can arise during fabrication of the devices (e.g. during an etch release step wherein one or more layers of a sacrificial material encapsulating the MEM device are removed to free the device for operation), or during use whenever surfaces of mechanical or electrically-active members of the MEM device come into contact.
Present ICs and MEM devices having on-board circuitry generally employ multiple levels of patterned metallization that can obscure lower electrical conductor levels, thereby complicating failure analysis or qualification testing from a device side (i.e. a top side) whereon the levels of patterned metallization are formed. Additionally, flip-chip packaging of ICs or MEM devices can make device-side analysis difficult, if not impossible. As a result, there is a need for the development of analysis methods that can operate on both a device-side and a substrate-side (i.e. a bottom side) of the ICs or MEM devices to be tested, thereby facilitating the detection of any open-circuit and short-circuit defects in the ICs or MEM devices.
Unfortunately, presently available substrate-side analysis methods are not totally effective in localizing open and shorted conductors. Furthermore, the presently available methods can be time consuming; they can yield a great deal of superfluous information; and they can provide only indirect evidence of open-circuit and short-circuit defects. What is needed is a rapid, sensitive method for analyzing ICs and MEM devices, with or without on-board circuitry, for open-circuit and short-circuit defects that operates under any mounting configuration.
An advantage of the apparatus and method of the present invention is that a high sensitivity for analyzing an IC or MEM device for any short-circuit defects therein can be realized by biasing the IC or MEM device with a constant-current source and measuring a change in a variable voltage of the source in response to a change in power demand by the IC produced upon irradiating a particular defect with a focused and scanned laser beam.
Another advantage is that, in some embodiments of the present invention for analyzing MEM devices, an induced voltage can be produced directly in the MEM device so that the constant-current source can be omitted.
Yet another advantage of the apparatus and method of the present invention is that any short-circuit defects can be located within an IC or MEM device from either a device side (i.e. a top side) or a substrate side (i.e. a bottom side) thereof.
Still another advantage of the present invention is that an entire die can be examined in a single image to locate any short-circuit defects therein.
Yet another advantage of the present invention is that it is nondestructive and can be used for qualification testing of ICs and MEM devices to locate any short-circuit defects therein. In the case of MEM devices when the short-circuit defects result from stiction, post-processing can be used to remove the stiction and thereby eliminate the short-circuit defects.
These and other advantages of the method of the present invention will become evident to those skilled in the art.
SUMMARY OF THE INVENTION
The present invention relates to a thermally-induced voltage alteration (TIVA) apparatus and method for analyzing a microelectromechanical (MEM) device formed on a substrate for any short-circuit defects therein. The TIVA apparatus in one embodiment thereof comprises a laser producing a laser beam; means for focusing and scanning the laser beam to irradiate a portion of the MEM device and thereby generate an induced voltage at the location of any short-circuit defects therein, the focusing and scanning means further providing a position signal to indicate the location of the laser beam on the irradiated portion of the MEM device; and means, comprising inputs of the induced voltage and the position signal, for indicating the location of each short-circuit defect within the irradiated portion of the MEM device. Although the substrate holding the MEM device can be formed of any suitable material (e.g. a semiconductor or a glass), the present invention is particularly suitable for analyzing MEM devices comprising a plurality of stacked layers of polycrystalline silicon formed on a silicon substrate.
The means for focusing and scanning the laser beam can comprise, for example, a scanning optical microscope. The means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device can comprise, for example, a display or a computer, and can further include an image processor.
The TIVA apparatus can further comprise a stage for holding the MEM device, with the stage optionally including means for heating or cooling the MEM device. Additionally, the TIVA apparatus can include a switch matrix, connected between the MEM device and the means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device, for selecting among a plurality of electrical connections to the MEM device (e.g. to select among a plurality of electrically-active members in the MEM device). The switch matrix can be operated manually or by computer control. The TIVA apparatus can also comprise a voltage amplifier, connected between the MEM device and the means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device, for amplifying the induced voltage. The voltage amplifier, which provides an increased sensitivity for detection of any short-circuit defects in the MEM device, can be either alternating-current (ac) coupled or direct-coupled (dc) coupled. Finally, the TIVA apparatus can comprise a photodetector (e.g. a silicon or germanium photodetector) for detecting a portion of the laser beam reflected or scattered from the MEM device. An electrical signal generated by the photodetector can be provided to the indicating means to generate a reflected-light image of the irradiated portion of the MEM device. This reflected-light image can then be superposed in the indicating means with a generated image of each short-circuit defect to provide for precise location of the short-circuit defects within the MEM device.
The laser in the TIVA apparatus can be selected to provide a wavelength for the laser beam that is in the range of 0.3 &mgr;m to 2.5 &mgr;m, depending upon whether the laser beam is to irradiate the MEM device from a top side of the substrate proximate to the MEM
Cole, Jr. Edward I.
Walraven Jeremy A.
Hohimen John P.
Nguyen Vinh P.
Sandia Corporation
LandOfFree
Thermally-induced voltage alteration for analysis of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thermally-induced voltage alteration for analysis of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermally-induced voltage alteration for analysis of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2949914