Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Using radiant energy
Reexamination Certificate
2000-09-18
2004-01-13
Deb, Anjan K. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Using radiant energy
C324S754120, C324S523000, C257S053000
Reexamination Certificate
active
06677760
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of and apparatus for analyzing a failure in semiconductor devices such as large scale integrated (LSI) devices.
2. Description of the Background Art
In semiconductor devices such as LSI devices, as the miniaturization of elements and the degree of integration increase, the number of interconnection levels of a metal interconnection structure increases. In high-performance LSI devices, with the increasing number of electrode pads, a so-called flip-chip structure in which electrode pads are formed not only around a chip but also in the chip has been mainstream. Such trends toward the increase in the number of interconnection levels of the metal interconnection structure and toward the flip-chip structure of the LSI devices make it impossible to conventionally analyze failures by accessing the chip (or wafer) through its upper surface by the use of a charged particle beam, such as an electron beam and an ion beam, or visible light. It is hence essential to employ failure analysis techniques which access the chip through its bottom surface (backside or opposite main surface from the device). An effective one of the failure analysis techniques of the backside accessing type includes a laser-induced current analysis (Infrared-Optical Beam Induced Current (IR-OBIC) analysis) technique utilizing a near-infrared laser beam. An example of the OBIC analyses by accessing the chip through its backside is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-136240 (1993).
Light having energy not greater than the band gap energy of silicon, i.e. light having a wavelength of not less than 1 &mgr;m can penetrate into a silicon substrate to some extent. The backside of the chip is irradiated with a near-infrared laser beam, and a change in current observed in synchronism with the scanning of the beam is converted into brightness to produce a current image. The IR-OBIC analysis obtains information about a failure-containing region in the chip, based on the current image.
The observed current is changed by photoexcitation and thermal excitation of electrons and holes which are caused by laser beam irradiation. Electron-hole pairs photoexcited near the pn junction in the silicon substrate are observed as photoinduced current to allow the manifestation of the pn junction, the detection of a junction leakage site, the detection of a gate leakage site, and the like. Selective photoexcitation of electrons or holes in metal interconnect lines allows the manifestation of a Schottky barrier. This permits the detection of in-process discrepancies, e.g. a faulty site at a contact between a metal interconnect line and the silicon substrate which results from the depletion of a dopant. On the other hand, the thermal excitation may be used to detect high-resistance sites such as voids and interface layers in the metal interconnect lines or contact holes. This utilizes the phenomenon that heat generated at a high-resistance site generates thermally-induced current and a resistance change, and a resultant change in observed current appears in the current image.
FIG. 17
is a block diagram of a background art apparatus for analyzing a failure in a semiconductor device. The background art apparatus, as shown in
FIG. 17
, comprises a laser beam source
101
, a laser beam controller
102
, a DC power supply
104
, a current detector
105
, a main controller
107
, and a display
108
. A laser beam source which generates a laser beam having a wavelength of about 1.1 &mgr;m or about 1.3 &mgr;m is commonly used as the laser beam source
101
. When using the laser beam source
101
which generates the laser beam of about 1.1 &mgr;m in wavelength, the apparatus can analyze all of the above-mentioned failure modes (i.e., a pn junction defect, a Schottky junction defect, and a faulty site in the metal interconnect line and the like). When using the laser beam source
101
which generates the laser beam of about 1.3 &mgr;m in wavelength, the apparatus can analyze the Schottky junction defect and the faulty site in the metal interconnect line and the like among the above described three failure modes.
A conventional method of analyzing a failure by the use of the apparatus of
FIG. 17
is described below. The laser beam source
101
generates a laser beam B
101
based on a control signal S
101
from the main controller
107
. The laser beam controller
102
controls the path of the laser beam B
101
based on a control signal S
102
from the main controller
107
, and scans a laser beam B
102
across the backside of a sample
103
. The current detector
105
detects current caused to flow in the sample
103
by the application of a predetermined voltage from the DC power supply
104
and the irradiation with the laser beam B
102
from the laser beam controller
102
, to input the detected current as data D
101
to the main controller
107
. Based on the data D
101
, the main controller
107
converts a change in current into brightness to produce a current image in the form of a two-dimensional image. The produced current image is inputted as data D
102
to the display
108
, and is then displayed on a screen of the display
108
.
The background art apparatus and method can two-dimensionally determine a failure-containing region in a chip by reference to the produced current image. By reference to the current image only, however, it is difficult to specifically diagnose and localize a failure in the chip, that is, to determine where the failure occurs in the chip in three dimensions or whether the failure is the pn junction defect, the Schottky junction defect or the fault in the metal interconnect line.
SUMMARY OF THE INVENTION
A first aspect of the present invention is intended for a method of analyzing a failure. According to the present invention, the method comprises the steps of: (a) irradiating a sample with a laser beam; (b) detecting a current generated in the sample as a result of the irradiation with the laser beam; and (c) analyzing a failure in the sample, based on detection results obtained in the step (b) when the sample is irradiated with the laser beam at respective different wavelengths.
Preferably, according to a second aspect of the present invention, in the method of the first aspect, the sample is irradiated with laser beams of about 1.1 &mgr;m, about 1.3 &mgr;m, and not less than 2.0 &mgr;m in wavelength, respectively, in the step (c).
Preferably, according to a third aspect of the present invention, in the method of the first aspect, the step (a) comprises the steps of: (a-1) scanningly irradiating the sample with the laser beam, and (a-2) fixedly irradiating a specific site of the sample with the laser beam, one of the steps (a-1) and (a-2) being selectively executed. The step (c) comprises the steps of: (c-1) determining a failure-containing region in which some form of failure occurs, based on a detection result obtained in the step (b) when the step (a-1) is executed; and (c-2) analyzing the cause of the failure in the failure-containing region, based on detection results obtained in the step (b) when the wavelength of the laser beam is changed while the failure-containing region is fixedly irradiated with the laser beam in the step (a-2).
Preferably, according to a fourth aspect of the present invention, in the method of the third aspect, the current is detected in the step (b) at a plurality of timed instants after irradiation of the failure-containing region with the laser beam, the plurality of timed instants being respectively corresponding to time constants of the current, the time constants being different from each other in excitation source of carriers generated by the irradiation with the laser beam.
A fifth aspect of the present invention is intended for a method of analyzing a failure. According to the present invention, the method comprises the steps of: (a) irradiating a sample with a laser beam of a predetermined wavelength; (b) applying a voltage to the sample; (c) de
Deb Anjan K.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Renesas Technology Corp.
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