JP5239163B2 - Thin film capacitor inspection method and apparatus - Google Patents

Description

  The present invention relates to a capacitor inspection method and apparatus, and more particularly, to a capacitor inspection method and apparatus suitably used in a semiconductor device or for specifying a failure location of a thin film capacitor used as a mounting component.

With the recent increase in speed and frequency of semiconductor devices, the role of decoupling elements that suppress the propagation of noise due to simultaneous switching of semiconductor devices into the circuit has become increasingly important. In particular, in a capacitor used for a decoupling element, a capacitance to a semiconductor device is increased in order to realize quick charge compensation with respect to a voltage variation at the same time as an increase in capacitance per unit area due to higher integration of the semiconductor device. There is a demand for minimizing the inductance component of the element itself. Against this background, thin film capacitors that are superior in thickness and integration have been developed compared to conventional chip components. Such a thin film capacitor generally has a configuration in which electrode layers and dielectric layers are alternately laminated, processed into a desired pattern, and the pattern area becomes a large area of 1 mm ² or more in order to ensure capacitance. There is.

  As a method for inspecting the thin film capacitor, generally, electrical connection is made to a capacitor electrode, and leakage current measurement or capacitance measurement is performed under a constant temperature environment. This method makes it possible to determine the quality of the capacitor as a whole. However, the failure of thin film capacitors can be caused by various causes such as dust in the process, defects in lithography, and non-uniformity of dielectric and electrode materials themselves. Even if it is found, it is impossible to identify the defective place or the cause of occurrence. Therefore, there is a problem that the identification of a capacitor defect does not lead to a specific process improvement for eliminating the defect, particularly in a large-area capacitor. Under such a background, it is desired to realize an inspection method for linking capacitor evaluation in a local region and its result with capacitor failure.

As a method for evaluating a capacitor in a local region, Patent Document 1 describes a method in which a groove is formed in a capacitor electrode with a scanning probe microscope (SPM) and the capacitor is divided, and then an SPM cantilever is used as a measurement probe. Patent Document 2 describes an apparatus that measures the temperature coefficient of the nonlinear dielectric constant in a minute region by irradiating laser light. An inspection method using laser light for local heating is used as an inspection method for wiring of a semiconductor device. Further, Patent Documents 3 to 6 describe methods and apparatuses for measuring a wiring by connecting a voltage source and a measuring device to a part of the wiring and matching timing with laser light irradiation.
JP 2004-134659 A JP-A-8-75805 (FIG. 3) JP-A-8-160095 (FIG. 1) Japanese Patent Laid-Open No. 9-257882 Japanese Patent Laid-Open No. 10-50784 JP 2004-191282 A

  However, there are some problems in applying the inspection methods and apparatuses described in the above patent documents to the inspection of thin film capacitors.

  The method using the SPM described in Patent Document 1 has a problem that the electrodes must be divided. The SPM cantilever itself contacts only in a very small area, but the capacitor electrode has the same potential. Therefore, the entire capacitor is measured only by the contact of the cantilever. For this reason, in order to limit a measurement position, it is indispensable to divide an electrode. By dividing the electrode in this way, the measurement target is already different from the actual capacitor structure, and it is impossible to detect a defect existing in the divided boundary region. There is also the possibility of causing new defects that cannot occur in the device fabrication process. Therefore, in this method, it is practically difficult to identify a defective portion formed in the thin film capacitor manufacturing process. Although a method of making the cantilever conductive and directly contacting the dielectric layer is also conceivable, this cannot reproduce the state of the actual electrode / dielectric interface, and the target capacitor cannot be evaluated.

  In patent document 2, the local area | region information is included in the measurement result by using together the local heating by a laser beam. However, the method and apparatus described in this document relate to the measurement of physical property values of the dielectric layer, and there is no description or suggestion regarding whether or not the measurement result is defective as a device. However, it cannot be used for inspection of the target thin film capacitor.

  In Patent Documents 3 to 6, for example, as shown in FIG. 5, a constant voltage is applied from a constant voltage source 32 to both ends of a wiring 33 in a semiconductor device, and laser light 31 is locally supplied from the surface side of the semiconductor device. The method of detecting the short circuit of a wiring and the defective location in wiring is described by measuring by the detector 34 the current change which flows through the wiring 33 with a detector. However, these documents only describe a wiring test method and an inspection apparatus, and do not describe or suggest a thin film capacitor inspection or determination method.

  The present inventors conducted experiments in which the methods described in Patent Documents 3 to 6 were applied to inspection of thin film capacitors. As a result, although the above method can detect defects in thin film capacitors that are in a completely short-circuited state, there are actually many defects in thin film capacitors that do not lead to complete short-circuiting, and such defects can be detected. There was a problem that could not be done. In addition, since a high applied voltage of several volts or more is required, the thin film capacitor breaks down due to the current that flows when the laser is irradiated to the defective portion, and thereafter another defective portion cannot be detected. Therefore, this technique cannot be applied to the inspection of a thin film capacitor which is an object of the present invention.

  As described above, in the conventional inspection method and apparatus, the defective state of the detectable capacitor is due to the inspection in a state different from the actual device structure or the diversion of inspection techniques other than the thin film capacitor. There was a big limitation.

  The present invention has been made in view of the above-described problems of the prior art, and provides a new local region inspection method for a capacitor to alleviate the above limitation in the prior art. That is, the object of the present invention is to inspect the thin film capacitor without destroying the thin film capacitor in the structure used in an actual device in order to facilitate the estimation of the failure point in the thin film capacitor and the improvement of the manufacturing process. It is an object of the present invention to provide a capacitor inspection method and apparatus for identifying a defective portion that is substantially undetectable.

In order to achieve the above object, a method for inspecting a capacitor according to the present invention includes a step of sequentially irradiating each region of the capacitor with a laser beam and locally heating the irradiated region.
During the laser light irradiation, applying an AC voltage between the electrodes of the capacitor to measure the capacitance, obtaining a capacitance measurement value corresponding to each irradiation region;
A step of comparing the measured values of the capacitances corresponding to the respective irradiation areas with each other between the irradiation areas.

Further, the capacitor inspection apparatus of the present invention includes a light source that generates a laser beam capable of irradiating a partial region of the capacitor to be inspected,
Scanning means for scanning each region of the capacitor with the laser beam;
Voltage application means for applying an alternating voltage between the electrodes of the capacitor in response to the scanning of the laser beam;
Measuring means for measuring the capacitance of the capacitor corresponding to the scanning region in accordance with the applied AC voltage.
Further, another capacitor inspection apparatus of the present invention includes a light source that generates laser light capable of irradiating a partial region of a capacitor to be inspected,
Scanning means for scanning each region of the capacitor with the laser beam;
Voltage application means for applying an alternating voltage between the electrodes of the capacitor in response to the scanning of the laser beam;
Measuring means for measuring the capacitance of the capacitor corresponding to the scanning region according to the applied AC voltage;
Data processing means for comparing the measured capacitance values corresponding to the scanning areas with each other between the scanning areas;

  According to the method and apparatus for inspecting a capacitor according to the present invention, an AC voltage is applied to the capacitor in response to local heating of the capacitor using laser light, and the capacitance can be measured. For this reason, it is possible to detect a defective state that cannot be detected by the conventional inspection method and does not reach a complete short-circuit state, and to specify its position. In addition, by setting the voltage applied to the capacitor to a low voltage, it is possible to suppress the occurrence of dielectric breakdown of the capacitor under inspection. Therefore, it is possible to specify the plurality of defects even in a capacitor having a plurality of defective portions. Moreover, since the destruction of the capacitor under inspection can be suppressed, there is an effect that it can be used even during the manufacturing process.

  The inspection method of the present invention further includes the steps of measuring the frequency dependence of the capacitance in advance without laser light irradiation and determining the frequency of the AC voltage for measuring the capacitance corresponding to the irradiation region. Also good.

  Further, in the step of obtaining a capacitance measurement value corresponding to each irradiation region, an AC voltage having a plurality of frequencies is applied between the electrodes of the capacitor using a frequency variable AC power source, and the respective irradiation regions are compared with each other. In the step of performing, each irradiation region may be compared for each measurement frequency.

  Further, the laser beam irradiation in each irradiation region may be performed intermittently.

  Further, in the step of comparing the measured capacitances with each other between the irradiation regions, the capacitance measurement value or the difference between the measurement values may be converted into luminance information or color information and displayed.

  In the capacitor inspection apparatus of the present invention, the voltage application means may generate an AC voltage having a variable frequency.

  Further, the light source may intermittently irradiate each irradiation region of the laser light.

  Furthermore, it may further include display means for converting the measured value of the capacitance measured by the measuring means or the difference between the measured values into luminance information or color information and displaying it together with the measurement frequency.

  In order to facilitate understanding of the present invention, the principle of the present invention will be described prior to the description of the embodiments of the present invention. As a result of investigating the causes of a number of defective portions that do not lead to complete short-circuiting, the measured capacitance has an abnormal value different from the capacitance inherently given by the dielectric material at a specific frequency or lower. It has been found that the frequency of showing and its abnormal value is in a frequency range lower than the resonance frequency of the capacitor. This is presumably because there is a relaxation time and slow polarization different from ionic polarization and electronic polarization that are the origin of the intrinsic capacitance of the dielectric crystal. Although the cause is not necessarily clarified, it is considered that electric dipoles are formed in the dielectric material due to impurities and lattice defects. Thus, the polarization that originally differs from the dielectric material has a temperature dependence of the polarization value different from the temperature dependence of the intrinsic capacitance of the dielectric material. Therefore, if only the defective part in the capacitor is heated and the capacitance of the thin film capacitor is measured, a measured value different from that obtained when the normal part is heated can be obtained. In view of this, each region of the thin film capacitor is scanned with a laser beam, and the capacitance of the capacitor is measured at an appropriate frequency in response to the laser irradiation of each irradiation region, and a defective portion in the capacitor is specified.

  In the measurement of the capacitance, the response to the alternating electric field of the polarization that causes the defect is measured by applying the alternating voltage. In general, the amplitude of the applied voltage is 1 V or less, and the load on the capacitor is small compared with the case where a DC voltage of several volts or more is applied to the capacitor film that is an insulator. It is possible to suppress dielectric breakdown. Therefore, even when there are a plurality of defective portions in the thin film capacitor, it is possible to suppress the dielectric breakdown of the capacitor at the defective portion scanned first, so that the remaining region is continuously scanned to detect another defective portion. It becomes possible. In addition, since the measurement capacitor can be prevented from being broken, measurement can be performed even during the manufacturing process of the product, for example, after the capacitor is formed and before the cover film is formed, so that selection of elements and feedback of process defects in a short time are possible.

  It is preferable to measure the frequency dependence of the capacitance of the thin film capacitor in advance without irradiating the laser beam and identify the frequency region where the capacitance abnormality at the defective portion is observed. This method makes it possible to subsequently perform capacitance measurement for identifying a defective portion at a single frequency, and is effective in shortening the measurement time. When the capacitance of the defective portion has a great influence on the capacitance of the entire thin film capacitor, the abnormal characteristics can be observed as the characteristics of the entire thin film capacitor without irradiation with laser light. In such a case, it is possible to measure the capacitance of the entire thin film capacitor in advance, identify the frequency region where the abnormality is observed, and determine the measurement frequency in advance.

  The method of measuring the capacitance of each irradiation area at multiple frequencies while irradiating with laser light clearly determines the appropriate frequency area for identifying the defective part from the capacitance measurement of the thin film capacitor measured without laser light irradiation. It is effective when it is not possible. This is because even if the capacitance of the defective portion does not have a large influence on the capacitance of the entire thin film capacitor, the difference from the normal region is often clarified by heating the defective portion with laser light. Furthermore, intermittently irradiating laser light is effective in that when the capacitance is measured at a plurality of frequencies in each irradiation region, the irradiation region is overheated and the temperature of the irradiation region can be prevented from changing for each measurement. There is.

  In any of the methods, it is easy to visually detect a defective portion by associating the position information of the laser light irradiation region with the measurement value and converting the measurement value into luminance information or color information for display. Effective in terms.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram for explaining the principle of the present invention. The capacitor 15 includes an upper electrode 12, a dielectric 13, and a lower electrode 14, and each region is sequentially scanned by the laser beam 11. Reference numeral 16 indicates a defective area in the capacitor 15, and reference numeral 17 indicates a normal area in the capacitor 15. The capacitance measuring device 18 applies an AC power source having a variable frequency between the upper electrode 12 and the lower electrode 14, and measures the capacitance of the capacitor 15 corresponding to the irradiation region of the laser beam 11.

  FIG. 2 is a graph showing characteristics of the frequency dependence of the capacitance of the normal region and the defective region of the capacitor measured by the method of FIG. FIG. 4A shows a change in capacitance when the normal region is irradiated with laser light, and FIG. 4B shows a change in capacitance when the defective region is irradiated with laser light. In these figures, the horizontal axis represents frequency, and the vertical axis represents capacitance per unit area. The symbols shown in the figure are Cn (T, f) and Ca (T, f), respectively, where the capacitance per unit area of the normal region and the defective region measured when the ambient temperature is T and the measurement frequency is f. Yes. ΔT is the temperature rise in the irradiation region of the capacitor, which rises from the ambient temperature T due to laser light irradiation. As shown in the figure, in the normal region irradiation, the capacitance increases uniformly at each measurement frequency depending on the temperature change ΔT of the irradiation region, but in the defective region, a large capacitance at a specific measurement frequency. An increase is observed.

When a thin film capacitor to be inspected has a defective region, the thin film capacitor 15 can be regarded as a capacitor in which the normal region 17 and the defective region 16 are parallel in terms of an equivalent circuit. When the electrode areas of the normal region and the defective region are Sn and Sa, respectively, and the symbols shown in FIG. 2 are used, the capacitance C0 measured at the measurement frequency f when the laser beam is not irradiated at the ambient temperature T is expressed by the following formula ( As shown in 1).
[Equation 1]
C0 (T, f) = Cn (T, f) .Sn + Ca (T, f) .Sa (1)

The thin film capacitor is irradiated with a laser beam such as an argon ion laser while sequentially changing the irradiation position. A laser irradiation apparatus in which the irradiation area of laser light is sufficiently smaller than the total area of the thin film capacitor is used. In this way, a temperature increase ΔT occurs only in the laser light irradiation region. Assuming that the area of the laser light irradiation region is δS, the measured capacitance C1 is expressed by Equations (2) and (3) in the cases where the laser light irradiation regions are all normal regions and all are defective regions, and the difference ΔC is expressed by Equation (2). (4)
[Equation 2]
C1 (T, f) = Cn (T, f) ・ (Sn−δS) + Cn (T + ΔT, f) ・ δS + Ca (T, f) ・ Sa (2)
C1 (T, f) = Cn (T, f) .Sn + Ca (T, f). (Sa-.delta.S) + Ca (T + .DELTA.T, f) .delta.S (3)
ΔC (T, f) = {Cn (T + ΔT, f) −Cn (T, f) + Ca (T, f) −Ca (T + ΔT, f)} · δS (4)

Since the origin of the failure-causing polarization and the normal polarization of the normal dielectric material are different, the temperature dependence of their capacitances is different. For this reason, if an appropriate frequency f0 is selected,
[Equation 3]
Cn (T + ΔT, f0) −Cn (T, f0) ≠ Ca (T + ΔT, f0) −Ca (T, f0) (5)
And ΔC (T, f0) ≠ 0. Accordingly, the defective region 16 and the normal region 17 can be discriminated by sequentially scanning each irradiation region with the laser beam 11, measuring the capacitance of the capacitor 15 each time, and performing comparison. The difference in the temperature change of the capacitance between the normal region 17 and the defective region 16 appears even if the defective region is not completely close to a short circuit if there is polarization related to the cause of failure or carriers that are thermally excited. Thus, it is possible to detect defects that could not be detected by DC measurement using a conventional constant voltage source.

  An example of an inspection apparatus capable of realizing the above inspection method will be described. FIG. 3 is a block diagram showing a configuration of an inspection apparatus according to an embodiment of the present invention. The inspection apparatus 20 includes a sample stage 23 on which a sample 22 on which a thin film capacitor to be inspected is formed is mounted. The capacitor in the sample 22 is provided with an inspection pad connected to an electrode, and is connected to an external wiring through a package. The laser beam 21 is generated by the laser generator 26, the irradiation position is scanned by the laser scanning unit 25, and each region of the sample 22 can be irradiated by the microscope unit 24 with an appropriate diaphragm. An impedance analyzer 27 having a frequency variable voltage source and a measurement / analysis function is used to apply an AC voltage to the capacitor and measure the capacitance. Control of laser generation, scanning, capacitance measurement, data processing, and display is performed by a data processing and system control unit 28 using a computer.

  The method of scanning the irradiation region of the laser beam 21 on the sample 22 includes means for moving the sample stage 23 while fixing the irradiation position of the laser beam 21 in addition to the above-described means for changing the irradiation region of the laser beam itself. You may go on. Further, when the thin film capacitor is exposed during the manufacturing process of the sample 22, the same effect can be obtained even if the probe needle is directly contacted with the electrode of the thin film capacitor.

  When the frequency f0 for identifying the defective portion is unknown, if the capacitance measurement is performed at a plurality of frequencies in a state where the laser beam is not irradiated in advance using the apparatus shown in FIG. It is effective to decide. Furthermore, by irradiating a laser beam and performing capacitance measurement performed in each irradiation region at a plurality of frequencies, the frequency dependency of the capacitance becomes clearer and it becomes easier to determine whether the region is a defective region. From the inventors' study, measurement in the region of 100 Hz to 1 MHz is preferable. Moreover, if the inspection apparatus 20 is provided with a mechanism for intermittently irradiating laser light, overheating during measurement can be suppressed and more accurate measurement can be performed.

  The present invention is particularly effective when a ferroelectric or a similar substance is used as a capacitor dielectric. The principle when the present invention is applied to a ferroelectric capacitor will be described with reference to FIG. Ferroelectric materials have the characteristics that the capacitance becomes maximal at the phase transition point, the temperature dependence of the capacitance increases in the vicinity, and the phase transition point changes depending on the composition and stress. The solid line shows the frequency characteristic of the normal region, and the broken line shows the frequency characteristic of the defective region. In particular, when the phase transition point changes between a normal region and a defective region, the capacitance is measured at an appropriate ambient temperature T and temperature increase ΔT shown in FIG. As a result, the sign of the gradient differs in the change in capacitance according to the temperature change between the normal area and the defective area, and the difference is detected more sensitively. Therefore, in addition to defects caused by finely processed shapes such as dust and lithography, defects caused by non-uniform composition and residual stress can be detected using the method of the present invention.

  The inspection method and apparatus of the present invention is not limited to the measurement of thin film capacitor components, but is a semiconductor memory in which the thin film capacitor is used, for example, a dynamic random access memory (DRAM) or a ferroelectric nonvolatile memory (FeRAM). It is also applicable to the measurement. Each capacitor is smaller than the laser light irradiation area, but by creating and inspecting a test pattern of a parallel capacitor having the same shape as the memory cell array, it is possible to select a specific capacitor in the cell array due to the etching or planarization process. It becomes possible to detect a defect appearing at a location by this inspection method.

  Further, the inspection object of the inspection method and apparatus of the present invention is not limited to a thin film capacitor, and the same effect can be expected in a capacitor in which a thick dielectric or electrode having a thickness of 1 μm or more is laminated.

  Although the present invention has been described based on the preferred embodiments thereof, the capacitor inspection method and apparatus of the present invention are not limited to the configurations of the above-described embodiments. Modifications and changes are also included in the scope of the present invention.

The typical sectional view for explaining the measurement principle in the method of the present invention. The graph which shows the frequency dependence of the capacitance of the normal area | region of a capacitor, and a defect area | region. The block diagram which shows the structure of the test | inspection apparatus which concerns on one Embodiment of this invention. The graph which shows the effect | action of a ferroelectric when the measurement of this invention method is applied to a ferroelectric capacitor. The block diagram which shows the test | inspection method of the conventional thin film capacitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 21 Laser beam 12 Upper electrode 13 Dielectric body 14 Lower electrode 15 Thin film capacitor 16 Defect area | region 17 Normal area | region 18 Capacitance measuring device 20 Inspection apparatus 22 Sample 23 Sample stand 24 Microscope part 25 Laser scanning part 26 Laser generation part 27 Impedance analyzer 28 Data processing, system controller

Claims (10)

Irradiating each region of the capacitor sequentially with laser light, and locally heating the irradiated region;
During the laser light irradiation, applying an AC voltage between the electrodes of the capacitor to measure the capacitance, obtaining a capacitance measurement value corresponding to each irradiation region;
And a step of comparing the measured values of the capacitance corresponding to the respective irradiation regions with each other between the irradiation regions.   The inspection of the capacitor according to claim 1, further comprising the step of measuring the frequency dependence of capacitance in advance without laser light irradiation and determining a frequency for measuring a capacitance measurement value corresponding to the irradiation region. Method.   In the step of obtaining a capacitance measurement value corresponding to each irradiation region, a step of applying an AC voltage having a plurality of frequencies between the electrodes of the capacitor using a frequency variable AC power source and comparing the irradiation regions with each other. Then, the inspection method of the capacitor according to claim 1 or 2 which compares between each irradiation field for every measurement frequency.   The capacitor inspection method according to claim 1, wherein the laser light irradiation is intermittently performed.   The step of comparing the measured capacitance with each other between the respective irradiation areas displays the capacitance measurement value or the difference between the measurement values by converting them into luminance information or color information and displaying them. The method for inspecting a capacitor according to 1. A light source that generates laser light capable of irradiating a partial region of the capacitor to be inspected;
Scanning means for scanning each region of the capacitor with the laser beam;
Voltage application means for applying an alternating voltage between the electrodes of the capacitor in response to the scanning of the laser beam;
And a measuring means for measuring the capacitance of the capacitor corresponding to the scanning region in accordance with the applied AC voltage.   A light source that generates laser light capable of irradiating a partial region of the capacitor to be inspected;
  Scanning means for scanning each region of the capacitor with the laser beam;
  Voltage application means for applying an alternating voltage between the electrodes of the capacitor in response to the scanning of the laser beam;
  Measuring means for measuring the capacitance of the capacitor corresponding to the scanning region according to the applied AC voltage;
  A capacitor inspection apparatus comprising: data processing means for comparing capacitance values corresponding to the scanning regions with each other between the scanning regions. The said voltage application means is a test | inspection apparatus of the capacitor of Claim 6 or 7 which generate | occur | produces the alternating voltage of a variable frequency. The said light source is a test | inspection apparatus of the capacitor as described in any one of Claims 6-8 which performs irradiation of the laser beam to each irradiation area | region intermittently. 10. The display device according to claim 6 , further comprising a display unit configured to convert the measured value of the capacitance measured by the measuring unit or a difference between the measured values into luminance information or color information and display it together with the measurement frequency. The capacitor inspection apparatus as described.

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