System and Method for Detecting Defects in an Interlayer Dielectric of a Semiconductor Device

The present invention generally relates to a system and method for detecting defects in an interlayer dielectric between conductive lines of a semiconductor device.

There is an increasing demand for miniaturization in the integrated circuits industry. This demand has led to an ever constant reduction in separation between conductive lines (e.g., metal lines) in order to reduce integrated circuit size and/or increase density. The reduced spacing between the conductive lines has the undesirable effect of increasing the capacitance of whatever material lies between the conductive lines. This phenomenon is known as capacitive crosstalk.

In the past, overall integrated circuit (IC) performance depended primarily on device properties, however, this is no longer the case. Parasitic resistance, capacitance and inductance associated with interconnections and contacts of an IC are beginning to become increasingly significant factors in IC performance. In current IC technology, the speed limiting factor is no longer device delay, but the resistive-capacitive (RC) delays associated with the conductive interconnections (e.g., metal lines) of the IC.

Conventional ICs typically employ an interconnect structure wherein a first conductive line is adjacent a second conductive line. If the crosstalk or capacitance between the first conductive line and the second conductive line is high, then the voltage on the first conductive line alters or affects the voltage on the second conductive line. This alteration in voltage may result in the IC being inoperable as a result of misinterpreting logic zeros, logic ones and voltage levels, and consequently incorrectly processing binary and/or analog information.

In order to reduce capacitive coupling and therefore reduce capacitive crosstalk, low dielectric constant (low-K) materials have been developed to lie between conductive lines in order to insulate one conductive line from the other.

FIG. 1 illustrates a portion of a typical integrated circuit. An insulating layer is formed on a semiconductor substrate, both the insulating layer and substrate are generally indicated at 20. A conductive pattern 22 including conductive lines 24 is formed over the insulating/substrate layer 20. The conductive lines 24 are separated by interwiring spaces 26 formed on the insulating/substrate layer 20. A dielectric material 30 (e.g., silicon dioxide, spin on glass) is shown deposited over the conductive lines 24 and the interwiring spaces 26 so as to form an insulative barrier 32 (interlayer dielectric) between the conductive lines 24.

Dielectric materials such as silicon dioxide are susceptible to ion contamination and moisture penetration. Furthermore, current deposition and polishing techniques have not reached a level where contamination of the interlayer dielectric (ILD) is eliminated. Additionally, voids within the ILD may result due to an imperfect fabrication process. Contaminants are undesirable in the ILD because the contaminants may degrade the performance of the ILD and facilitate unwanted capacitive crosstalk (e.g., leakage) between adjacent metal lines. Voids are not desired because the voids weaken the ILD and may lead to the formation of cracks within the ILD which may also give rise to leakage of current between adjacent conductive lines.

Detection of such defects (e.g., lattice defects, dislocations, impurities, contaminants and voids) is typically performed at the end of the process line after the IC is substantially complete. However, the in-line fabrication of the IC represents up to 95% of the cost of the ultimate integrated circuit. Thus, it would be desirable to test the IC during fabrication in order to detect defects in the IC early on before additional monies and man hours are spent down the line for later fabrication steps.

In view of the above, it would be desirable to have a system and method for in-line detection of defects in the interlayer dielectric of an integrated circuit.

The present invention provides for a system and method for in-line detection of defects (e.g., lattice defects, dislocations, impurities, contaminants and voids) in an interlayer dielectric between adjacent conductive lines of an integrated circuit. More particularly, the present invention applies a bias voltage between adjacent conductive lines of an IC so as to induce a leakage current to flow between the adjacent conductive lines across the ILD separating the two conductive lines. The applied voltage is preferably applied at a level coincident with the operating voltage of the IC so as to avoid breakdown of any components of the IC. A radiation source or light source (e.g., ultraviolet (UV) laser) is applied at the portion of the ILD where leakage current flow is being induced. The light source provides for enhancing the flow of leakage current at the ILD portion being tested for defects. More particularly, by applying a light source (preferably UV) with an energy level greater than the energy barrier between the metal of the conductive lines and the dielectric (26 3.2 eV in the case of SiO.sub.2) carriers are injected into the dielectric from the metal. This results in the leakage current flow being enhanced to a level suitable for measurement thereof.

If defects (e.g., lattice defects, dislocations, impurities, contaminants and voids) are present with the portion being tested, the amount of leakage current flow detected will differ from an expected value if the defects were not present. This is because some types of defects may result in the presence of trapping sites within the ILD. As a result of the trapping sites less energy may be required to excite electrons across the band-gap than if the dielectric was free of trapping sites. The light source not being sufficient to excite carriers across the band-gap of the dielectric will generate carriers substantially only at the trapping sites. Accordingly, the presence of such type of defect in the ILD may increase the amount of current flowing across the dielectric as compared to if the defect were not present. Additionally, the defect site may create any energy barrier between the metal and dielectric which is less than 3.2 eV. In such a case, more carriers may be injected at the defect site. By selectively choosing the light energy to be less than 3.2 eV or close to 3.2 eV the impact on leakage current associated with a defective site as compared to a normal site is enhanced. With respect to voids, the amount of current flow detected will be less than if the voids were not present. Accordingly, by monitoring for a decrease in current below an expected level the presence of voids may be determined. Thus, by monitoring for a change in leakage current above and/or below an expected level the presence of defects in the ILD may be detected. By selectively scanning the light source across a predefined mapping grid of the ILD and simultaneously monitoring current flow the location of the defect may be determined with substantial accuracy.

As demands for miniaturization increase, resulting in the need for moving conductive lines even closer together, the present invention may be employed to detect defects in an ILD of an integrated circuit early on and avoid performing continued fabrication steps on a defective IC. Thus, the present invention provides for a system and method which quickly detects defects in an ILD in a non-destructive manner during in-line processing with substantial resolution and accuracy.

In accordance with one specific aspect of the present invention, a system for detecting defects in an interlayer dielectric (ILD) interposed between two conductive lines includes a processor for determining the presence of a defect in the ILD. The system also includes a leakage current inducement system for inducing a leakage current between the two conductive lines across the ILD; and a monitor operatively coupled to the processor. The monitor monitors a parameter at least related to the leakage current. The processor determines the presence of a defect in the ILD based upon the monitored parameter.

Another aspect of the present invention relates to a system for detecting defects in an interlayer dielectric (ILD) interposed between two conductive lines including a processor for controlling general operations of the system. The system additionally includes a voltage source adapted to apply a bias voltage between the two conductive lines and induce a leakage current across the ILD; and a light source for illuminating at least a portion of the ILD and enhancing the leakage current. The system also includes a current monitor for measuring the induced leakage current, the current source being operatively coupled to the processor; wherein the processor determines the existence of a defect in the ILD based on the measured leakage current.

Still yet another aspect of the present invention provides for a method for detecting defects in an interlayer dielectric (ILD) interposed between two conductive lines, including the steps of: inducing a leakage current between the two conductive lines across the ILD; measuring the leakage current; and determining the presence of a defect based on the measured leakage current.

According to another aspect of the present invention a system for detecting defects in an interlayer dielectric (ILD) interposed between two conductive lines includes: means for inducing a leakage current; means for monitoring the leakage current; and means for determining the presence of a defect in the ILD based upon the monitored leakage current.

In accordance with yet another aspect of the present invention, a system for detecting a three-dimensional location of a defect in an interlayer dielectric (ILD) interposed between two conductive lines lying adjacent each other along a plane includes a processor for controlling general operations of the system; a voltage source adapted to apply a bias voltage between the two conductive lines and induce a leakage current across the ILD; a light source for illuminating at least a portion of the ILD and enhancing the leakage current, the light source being selectively adjustable to incrementally apply a light beam at a desired wavelength from among a plurality of wavelengths; a current monitor for monitoring the leaking current; wherein the processor determines the existence of a defect in the ILD based on the monitored leakage current correlated with the applied wavelength of the light beam.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.

FIG. 1 is a schematic cross-sectional illustration of a portion of a semiconductor device fabricated in accordance with conventional techniques;

FIG. 2a is a schematic representation of part of a system for detecting defects in an ILD in accordance with the present invention;

FIG. 2b is a schematic representation of the partial system of FIG. 2a wherein a light beam is directed at a first portion of the ILD in accordance with the present invention;

FIG. 2c is a schematic representation of the partial system of FIG. 2a wherein a light beam is directed at a second portion of the ILD in accordance with the present invention;

FIG. 3a is a schematic block diagram of a system for detecting defects in an ILD in accordance with the present invention;

FIG. 3b is a schematic block diagram of another system for detecting defects in an ILD in accordance with the present invention;

FIG. 3c is a schematic block diagram of yet another system for detecting defects in an ILD in accordance with the present invention;

FIG. 3d is a schematic block diagram illustrating a system for directing a light beam at a selected portion of a device being tested in accordance with the present invention;

FIG. 3e is a schematic block diagram illustrating another system for directing a light beam at a selected portion of a device being tested in accordance with the present invention;

FIG. 4a is a schematic representation of part of a system for detecting defects in an ILD interposing two vertically adjacent conductive lines in accordance with the present invention;

FIG. 4b is a schematic representation of the partial system of FIG. 4a wherein a light beam is directed at a first portion of the ILD in accordance with the present invention;

FIG. 4c is a schematic representation of the partial system of FIG. 4a wherein a light beam is directed at a second portion of the ILD in accordance with the present invention;

FIG. 5 is a representative three-dimensional grid map of a portion of an ILD illustrating leakage current amplitudes taken at grid blocks of the grid map in accordance with the present invention;

FIG. 6 is a current amplitude table correlating the leakage current amplitudes of FIG. 5 with expected values for the leakage current amplitudes in accordance with the present invention; and

FIG. 7 is a flow diagram illustrating one specific methodology for carrying out the present invention.

The present invention relates to a system and method for detecting defects in an ILD by inducing a leakage current between conductive lines across the ILD. The presence of defects in the ILD will change the amount of leakage current above or below an expected value depending upon the nature of the defect. By monitoring the level of current in connection with the location of a light source being employed to enhance the leakage current, the location and nature of defect(s) in the ILD may be determined with substantial accuracy. Provided below is a more detailed description for carrying out this invention. The following detailed description is of the best modes presently contemplated by the inventors for practicing the invention. It should be understood that the description of these preferred embodiments are merely illustrative and that they should not be taken in a limiting sense.

The present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout.

Referring initially to FIGS. 2a-2c, a portion of a system for carrying out the present invention is schematically illustrated. The system 50 includes a light source (e.g., ultraviolet laser) 52 for directing a light beam of substantially uniform intensity at a portion of an ILD layer 54 interposed between two conductive lines 60a, 60b formed on a substrate/insulating layer 64. Both the insulating layer and substrate are illustrated in common for ease of understanding and are referenced by reference number 64. It will be appreciated that any light source suitable for carrying out the present invention may be employed and is intended to fall within the scope of the hereto appended claims. Preferably, the light source emits light of a wavelength greater than the absorptive wavelength of the ILD 54 so that the light penetrates deep enough into the ILD 54 to excite carriers therein.

As is known, the conductive lines 60a, 60b are part of a conductive pattern formed over the insulating/substrate layer 64. Preferably a metalization pattern is formed by depositing a metalization layer and patterning employing suitable photolithographic and etching techniques (e.g., anisotropic etching such as reactive ion etching). The conductive pattern may be deposited by any of a variety of suitable deposition techniques, such as chemical vapor deposition (CVD) processes including low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD), melting or sputtering. The conductive lines may include any suitable material (e.g. aluminum) for carrying out the present invention.

The conductive lines 60a, 60b are adjacent each other and provide necessary electrical connections between devices of an integrated circuit (not shown). Although only two conductive lines 60a, 60b are shown for ease of understanding, it is to be appreciated that many thousands or even millions more such conductive lines may exist in the integrated circuit. As noted above, the increasing demand for miniaturization in the integrated circuits industry has lead to an ever constant reduction in separation between the conductive lines 60a, 60b in order to reduce IC size. However, the reduced spacing between the conductive lines 60a, 60b has the undesirable effect of possibly increasing the capacitance of whatever material lies between the conductive lines 60a, 60b to result in capacitive crosstalk between adjacent conductive lines.

Since market forces are driving the integrated circuitry industry towards bringing the conductive lines 60a, 60b closer together in order to maximize substrate surface utilization, insulation having low dielectric constant is desired between the conductive lines 60a, 60b in order isolate the conductive lines 60a, 60b from one another and to lower capacitive coupling between the conductive lines 60a, 60b, respectively, and in turn reduce capacitive crosstalk. As noted above, the presence of defects in the ILD 54 may cause the resultant integrated circuit to malfunction.

The system 50 of the present invention provides for detection of such defects during in-line processing before a substantial amount of monies and man hours have been expended toward fabricating the integrated circuit. The system 50 further includes a voltage source 70 for inducing a leakage current between the conductive lines 60a, 60b across the portion of ILD 54a interposed between the conductive lines 60a, 60b. Preferably, the voltage source 70 applies a bias voltage (e.g., 3 eV) close to the final operating voltage of the resultant IC and desirably below the breakdown voltage of the resultant IC so as to avoid breakdown of various components of the prefabricated IC.

A current monitor 74 is placed in series with the voltage source 70 in order to monitor the amplitude of the induced leakage current. A processor 100 (FIG. 3a) is employed to monitor the level of leakage current. The processor 100 also controls the light source 52 so as to control the portion of the ILD 54 being illuminated and the energy level of the light being applied to the ILD 54. The light source 52 provides for enhancing the flow of the leakage current at the ILD portion being tested for defects. More particularly, by applying light with an energy level greater than the energy barrier between the metal of the conductive lines 60a, 60b and the dielectric carriers are injected into the dielectric from the metal in accordance with the photo hall-effect. The photo hall-effect is a well known phenomenon and thus detailed discussion related thereto is omitted for sake of brevity. The leakage current flow is enhanced to a level suitable for measurement thereof.

Thus, by selectively directing a light beam 102 at a portion of the ILD 54 and comparing the induced leakage current to an expected value, the system 50 can determine if a defect exists in the ILD 54 at the portion. Furthermore, by dividing the ILD 54 into a grid map of such ILD portions and selectively scanning the light beam 102 from one grid block to another grid block and taking corresponding current measurements, the present invention can determine the location and nature of such defects with substantial accuracy. FIG. 2b illustrates the light beam 102 being directed at a first location of the ILD 54 and FIG. 2c illustrates the light beam 102 being directed at a second location of the ILD 54. Leakage current measurements are taken at each location when the locations are being illuminated, respectively.

Turning now to FIG. 3a, a representative block diagram of the system 50 is shown and will now be discussed. The system 50 includes the processor 100 which is programmed to control and operate the various components within the system 50 in order to carry out the various functions described herein. The processor or CPU 100 may be any of a plurality of processors, such as the AMD K6 and other similar and compatible processors. The manner in which the processor 100 can be programmed to carry out the functions relating to the present invention will be readily apparent to those having ordinary skill in the art based on the description provided herein.

A memory 130 which is coupled to the processor 100 is also included in the system 50 and serves to store program code executed by the processor 100 for carrying out operating functions of the system 50 as described herein. The memory 130 includes read only memory (ROM) and random access memory (RAM). The ROM contains among other code the Basic Input-Output System (BIOS) which controls the basic hardware operations of the system 50. The RAM is the main memory into which the operating system and application programs are loaded. The memory 130 also serves as a storage medium for temporarily storing information such as induced leakage current values, light beam 102 location, light beam intensity, expected leakage current tables, and other data which may be employed in carrying out the present invention. For mass data storage, the memory 130 may include a hard disk drive (e.g., 10 Gigabyte hard drive).

The system 50 includes a power supply 140 which provides power to the system 50. Connections between the power supply 140 and other components of the system 50 are not shown for ease of understanding the present invention. Any suitable device or means (e.g., battery, line power) for powering the system 50 may be employed.

The system 50 includes a display 150 which is coupled to the processor 100 via a display driver circuit 152 as is conventional. The display 150 may be a color monitor or a flat screen liquid crystal display (LCD) or the like. The display 150 may be a fine pitch liquid crystal display operated as a standard CGA display with a suitable resolution. The display 150 functions to display data or other information relating to ordinary operation of the system 50. For example, the display 150 may display a set of discrete induced leakage current values for various portions of the ILD 54. Additionally, the display 150 may display a variety of functions indicating the operation of the system 50. The display 150 is capable of displaying both alphanumeric and graphical characters.

An operator input system 160 (e.g., keyboard and mouse) is also coupled to the processor 100, and provides for a user to interact with the system 50 as is well known in the art.

The system 50 may employ a neural network 164 (FIG. 3b) to facilitate data analysis and processing. The use of neural networks is well known in the art and thus further discussion relating thereto is omitted for sake of brevity. Alternatively, the system 50 may employ an expert system 166 (FIG. 3c) to facilitate data analysis and processing. Expert systems provide for classification based on inference to derive more knowledge about a subject and in turn employ logical reasoning in making a decision.

The current monitor 74 and voltage source 70 have been discussed above and detailed discussion related thereto is omitted for sake of brevity. It will be appreciated that any current monitor and/or voltage source suitable for carrying out the present invention may be employed and are intended to fall within the scope of the hereto appended claims. Furthermore, although the preferred embodiment employs the current monitor 74 to monitor the level of leakage current it is to be appreciated that one may monitor voltage levels, power levels, etc. which are functions of the level of leakage current. Such monitoring of parameters which are a function of or related to the leakage current are intended to be considered to fall within the scope of the present invention as defined by the claims.

FIG. 3d is a schematic block illustration of one technique for directing the light beam 102 at a desired portion of the ILD 54. A device 167 being tested for defects is placed on a moveable stage 169 which may be controlled by the processor 100. The processor 100 selectively controls movement of the stage 169 along a horizontal plane so that the light beam 102 is directed at a desired portion of the ILD 54. Alternatively, as shown in FIG. 3e rather than moving the device 167 being tested the processor 100 may control movement of the light source 52 and/or beam 102 so that the light beam 102 is directed at a desired portion of the ILD. It is to be appreciated that any suitable technique and/or device for directing the light beam 102 at a selected portion of the ILD 54 may be employed and is intended to fall within the scope of the attached claims.

FIGS. 4a-4c illustrate the system 50 of the present invention being employed to determine if any defects exist in an ILD 110 interposed between two vertically adjacent conductive lines 120a, 120b. As shown in FIGS. 4b and 4c, the light beam 102 may be directed at different portions of the ILD 110, and by dividing up the ILD 110 into a sufficient number of portions (e.g., grid blocks), the present invention can determine the location and nature of defects in the ILD 110 with substantial accuracy as described herein.

Turning now to FIG. 5 a three-dimensional representative illustration of a section of the ILD 54 divided into grid blocks 170 is shown which may be displayed on the display 150. The section of the ILD 54 is shown divided into one hundred and forty four grid blocks 170 along an X-Y plane which make up a grid map 172. The grid 172 includes twelve x-segments and twelve y-segments and thus is divided up into the grid blocks (X.sub.1 Y.sub.1 through X.sub.12 Y.sub.12) 170. Each grid block 170 is representative of a portion of the ILD 54 where the light beam is directed to enhance the leakage current flowing between conductive lines (e.g., 60a, 60b) across the ILD 54 between the conductive lines. Each grid block 170 is shown with a corresponding current amplitude signature taken when the light beam 102 was directed thereon respectively. As can be seen, the current amplitudes at each grid block is substantially the same (e.g., within an expected range) except for the current amplitude at grid block X.sub.7 Y.sub.6. The current amplitude at grid block X.sub.7 Y.sub.6 is larger than the current amplitude measured at the other grid blocks, respectively. Thus, a defect is likely to exist in the ILD 54 at the portion mapped by grid block X.sub.7 Y.sub.6. Since the current amplitude is larger than expected the defect is likely of the type which results in trapping sites in the ILD 54.

FIG. 6 is a representative table of current amplitudes (taken at the various grid blocks 170 when the light beam 102 was directed thereon) which have been correlated with expected current amplitude values for the portions of the ILD 54 mapped by the respective grid blocks 170. As can be seen, all of the grid blocks 170 except grid block X.sub.7 Y.sub.6 have current amplitudes corresponding to an expected current value (I.sub.E) (e.g., are within an expected range of current amplitudes), while grid block X.sub.7 Y.sub.6 has an unexpected current value (I.sub.U). Thus, the processor 100 has determined that a defect is likely to exist at the portion of the ILD 54 mapped by grid block X.sub.7 Y.sub.6.

If the current amplitude is above an expected range a defect in the ILD (e.g., lattice defect, impurity, dislocation, ion contaminant) which likely leads to the formation of a trapping site may exist. If the current amplitude is below an expected range a defect in the ILD such as a void, for example, may exist. It is to be appreciated that the memory 130 may store a plurality of tables which match particular leakage current signatures to various defects, and the processor 100 may access such tables to diagnose the type of defect that may exist. The use of the neural network 164 or expert system 166 may expedite grid analysis and defect diagnosis.

FIG. 7 is a flow diagram illustrating one particular methodology for carrying out the present invention. In step 200, the processor 100 performs general initializations to the system 50. In step 210, the processor 100 maps at least a portion of the ILD 54 between two conductive lines 60a, 60b into a plurality of grid blocks 170. In step 220, the processor 100 controls the voltage source 70 so as to apply a bias voltage between the two conductive lines 60a, 60b. In step 220, the processor 100 causes the light source 52 to direct the light beam 102 on a first grid block so as to facilitate inducement of a leakage current between the two conductive lines 60a, 60b, and the processor 100 measures the amplitude of the leakage current as the light beam is directed on the first grid block. This step is repeated "N" number of times until current measurements have been taken corresponding to the light beam directed on all "N" number of grid blocks, wherein "N" is an integer.

In step 230, the processor 100 determines if "N" number of current measurements have been taken. If yes, the processor 100 proceeds to step 240 where the measured current values are compared against a range of expected current values. In step 250, the processor 100 determines if any unexpected current values exist. If no, the processor 100 proceeds to step 260 where the testing process is complete. If yes, the processor 100 analyzes the unexpected current value, determines the grid block location of the defect, diagnoses the defect, determines the location of the defect, and notifies a user of the system 50 that a defect may exist, the location on the ILD 54 where the possible defect may reside and the probable nature of the defect (e.g., lattice defect, impurity, contaminant, dislocation, void). Then, the processor 100 proceeds to step 260 where the ILD test is complete in relevant part.

It is to be appreciated that another embodiment of the present invention may be employed to detect the location of a defect in the ILD 54 in a three-dimensional manner. More particularly, by selectively varying the wavelength of the light beam 102 being directed at the ILD 54, the depth of penetration of the light beam 102 into the ILD 54 may be controlled. By systematically varying the depth of penetration of the light beam 102 into the ILD 54 and taking leakage current measurements as described above, not only may the location of a defect be detected along an x-y plane but the depth of the defect along the z-axis may be determined as well.

The present invention provides for a system and method which quickly detects defects in an ILD in a non-destructive manner during in-line processing with substantial resolution and accuracy.

What has been described above are preferred embodiments of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.