JP3701470B2 - Charge measurement device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charge amount measuring device, and in particular, a conductor by an electrostatic charge charged on an insulator portion of a measurement object including an insulator and a conductor, such as an LSI package and a lead terminal. The present invention relates to a charge amount measuring apparatus effective for use in measuring the amount of charge induced in a portion or electrostatic energy.
[0002]
[Prior art]
In recent years, as seen in various LSIs, the progress of high-performance semiconductor devices and the accompanying increase in density has been remarkable, and the number of elements per chip has increased exponentially. Along with this, each element constituting the semiconductor device has become extremely small in size and its resistance to electric fields has been reduced. As an example, even in an LSI mounted on a household electrical product, the planar dimensions of elements constituting the LSI are becoming less than 1 μm, and for example, the gate insulating film thickness of a MOS transistor and the depth of a pn junction The dimension in the cross-sectional direction is also less than 0.05 μm. In addition to this, another factor that reduces the electrostatic breakdown resistance of semiconductor devices (hereinafter referred to as LSIs) is also commercializing products with a thin and large package with a thickness of 1 mm or less. In addition, the electrostatic capacity of the package, in other words, the amount of electrostatic energy held is increasing dramatically. Under such circumstances, preventing destruction of LSI due to static electricity has become a very important issue.
[0003]
As will be described later, the destruction of the LSI due to static electricity causes energy to be supplied to each structural part inside the LSI as the charge charged on the lead terminal moves, or the accumulated charge forms a strong electric field. However, the direct charge of the package plays an important role in the intermediate stage of the process leading to destruction. The following two modes are generally considered as a mechanism for charging and destroying the LSI during the manufacturing process or handling.
[0004]
The first mode is a direct discharge (spark discharge or contact discharge) from a high-voltage charged body outside the LSI to the lead terminal of the LSI, and the discharge energy or charge destroys the LSI. Examples of the high-voltage charged body include a TV CRT, a frictionally charged human body, and an insulator. Examples of the frictionally charged insulator include jigs and tools used in a manufacturing process such as a plastic magazine, and mounting parts such as a printed wiring board and an IC socket. Further, an LSI itself sealed with an insulating package such as resin or ceramic is also included.
[0005]
In the second mode, the insulating package is charged or charged, and the charge electrostatically induced in the metal lead terminal due to the charging is discharged toward the ground (in this case, spark discharge or contact discharge). It is destruction based on the supply of energy or the formation of a strong electric field. Therefore, the destruction of the LSI in this mode is closely related to the relative positional relationship between the LSI and the ground and the charge amount of the package. The charging of the package in this mode is inevitably caused by the handling of the LSI during the LSI manufacturing process or during the mounting operation, separately from the case where it occurs as a result of the discharge in the first mode. There is a case to do. That is, even if the discharge energy and the charge amount in the first mode are sufficient to destroy the micro structure portion inside the LSI, if the discharge time constant is long, the heat energy and the charge are concentrated inside the LSI. Does not occur and a large charge remains without destroying the LSI. On the other hand, in the LSI manufacturing process, especially in the assembly process and inspection process, usually called “post-process”, the LSI (enclosed in the package) is adsorbed and moved by a suction nozzle using high-pressure air, or a long rail There is always work to move it by sliding on it. At this time, the LSI package is charged by friction between the LSI and air or rail. In addition, frictional charging occurs when the LSI and the LSI rub against each other even when the LSI is housed in a case called a magazine. Further, even when the LSI is stationary, for example, in the low-temperature temperature characteristic inspection in the inspection process, dry air is blown to the LSI to prevent condensation, and in this case, the package is triboelectrically charged.
[0006]
With respect to the destruction in the first mode against the destruction of LSI due to static electricity as described above, conventionally, a protection circuit is added to or built in an LSI chip, and the device is devised and improved, and the human body represented by a wrist strap. Various measures have been taken, such as static elimination of charges or prevention of charging by an ionizer. The problem is countermeasures against destruction in the second mode, but whatever measures are taken, it is indispensable to accurately grasp the energy or charge amount that leads to charge breakdown of the LSI. The present invention has been made mainly based on such a need.
[0007]
In response to the necessity as described above, a charge amount (and hence electrostatic energy amount) measuring method or measuring apparatus whose main measurement object is limited to LSI has not been found so far. For these reasons, currently, measuring devices used in other technical fields have been used for measurement in LSI. For example, there is a well-known Faraday cage. This is an apparatus for measuring the amount of electrostatic charge charged on an object. As shown in FIG. 7A, this is the same as a cup-shaped metal plate 2 into which an object to be measured (for example, LSI) 1 is placed. It has a structure in which a dielectric 4 having a constant capacitance value C is sandwiched between a metal plate 3 having a core shape and ground potential. When the DUT 1 is placed in the cup-shaped metal plate 2 on the inner side, a potential difference V is generated between the metal plate 2 and the metal plate 3 due to electrostatic induction. Thus, the electrostatic charge amount Q of the DUT 1 is obtained by Q = CV. As is clear from the principle of operation of the Faraday cage, the Gauss's theorem is realized as it is. If, for example, an LSI is selected as the device under test 1, regardless of whether there is a lead terminal inside or not, it does not matter. The total electrostatic charge charged on the package surface can be measured.
[0008]
Japanese Patent Application Laid-Open No. 53-116182 discloses an electrostatic charge amount measuring apparatus characterized in that a self-discharge type static eliminator is used for a current collecting part for inducing an electrostatic charge of an object to be measured. . As shown in FIG. 7B, for example, the charge of the DUT 1 is induced in the brush-like self-discharge type static eliminator 6 and accumulated in the dielectric 4 having a constant capacitance value C. From the potential difference V and the capacitance value C at that time, the electrostatic charge amount Q of the object to be measured is measured by Q = CV. This device attempts to remedy the drawbacks of the Faraday cage, as described in the publication. That is, in the Faraday cage, due to its shape, the object to be measured must be sampled and brought into the cup-shaped metal. For this reason, if the object to be measured cannot be measured in its actual state, the shape of the object to be measured is limited, or the measurement object cannot be measured depending on the object to be measured, such as a long object. Furthermore, the measurement value fluctuates due to fluctuations in the occurrence of various frictions during sampling, and the measurement accuracy is not sufficient, but according to the electrostatic charge amount measuring device described in the above publication, the Faraday cage Such drawbacks are eliminated.
[0009]
If the Faraday cage or the electrostatic charge amount measuring device described in the above publication is used, it is possible to measure the total electrostatic charge amount of the charged LSI package, although some improvement and improvement are naturally necessary.
[0010]
[Problems to be solved by the invention]
As described above, if the electrostatic charge measuring device or Faraday cage disclosed in Japanese Patent Laid-Open No. 53-116182 is used, it is possible to measure the total electrostatic charge charged in the LSI package. The measurement result can be used for planning countermeasures for preventing electrostatic breakdown of LSI. However, when the measurement object is limited to the LSI, what causes electrostatic breakdown in the LSI is the formation of a strong electric field accompanying the accumulation of discharge energy or charge supplied to each structural part inside the LSI through the lead terminal. In consideration of this, not the total electrostatic charge charged in the LSI package, but the excess dynamic charge (described later) flowing through the lead terminal to the ground or the electrostatic energy accumulated in the stray capacitance between the lead terminal and the ground. In addition, direct measurement for each lead terminal is directly linked to prevention of electrostatic breakdown of the LSI. In the following, based on the research results of the present inventors, the concept of excessive dynamic charge and the role of the excessive dynamic charge in electrostatic breakdown in the second mode described above are described, and the effectiveness of the measurement of the excessive dynamic charge amount is described. Will be described.
[0011]
First, the concept of excess dynamic charge will be described. Excess dynamic charge is not a newly discovered charge or concept, but is the name of one of the electrostatic induction phenomena that appears at the beginning of many electromagnetism textbooks. When there is a charge amount Q in a space surrounded by a certain ground plane 7 as shown in FIG. 8A, the space includes a charge amount Q, a relative permittivity of a substance occupying the space, and a charge amount. An electric field determined by the distance between Q and the ground plane is formed, and the potential is determined for each location. Now, assume that a small neutral metal piece 8 is placed in this space. The potential of the metal piece 8 is the potential at that position before the metal piece is inserted.
[0012]
Next, as shown in FIG. 8B, when the metal piece 8 is grounded by the thin conductor 9, positive charges are transferred from the metal piece 8 to the ground 7 so that the potential at the positions of the metal piece 8 and the conductor 9 is zero. And the same amount of negative charge remains. Or, in the opposite expression, negative charges flow from the ground 7. Either expression may be used, but if both expressions are mixed, it will be misleading, so we will use the former “flow out” and name this charge “excess dynamic charge”. The amount of excess dynamic charge that flows when the metal piece 8 is connected to the ground 7 is an amount corresponding to the electric field that is determined after the metal piece 8 is connected to the ground 7. This amount is equal to the amount of negative charge remaining so that the potential of the metal piece 8 connected to the ground 7 becomes zero. As is clear from the above description, the excessive dynamic charge amount is closely related to the charged portion (position of the charge amount Q), the relative positional relationship between the metal piece 8 and the ground plane 7, and the charged charge amount Q. are doing. Therefore, when measuring the amount of excessive dynamic charges, the measurement object must be measured in the state where it should be.
[0013]
Next, FIG. 9 shows a model of destruction due to excessive dynamic charge of an LSI in which a package is charged based on the above concept. Referring to the figure, an insulating resin (package) 10 has two metal lead terminals 11L and 11R, and a pn junction (an LSI structure portion) connected by a metal wire 12 between them. An example) is arranged. The surface of the resin 10 is charged with a positive electrostatic charge due to friction during the manufacturing process or discharge in the first mode. In the figure, an image is shown in which negative charges are induced and fixed on lead terminals 11L and 11R, wires 12, and part of the chip by the electrostatic charges on the surface of the resin 10, and the positive charges become excessively moving charges. In the initial state, the left and right lead terminals 11L and 11R, the wire 12 and the pn junction are all at the same potential. Next, assuming that the right lead terminal 11R is at the ground potential due to spark discharge or contact discharge, all excess dynamic charges move at a very high speed toward the ground. The moving speed is determined by the distribution constant of the circuit, but even if the pn junction is in a breakdown state, it has a higher resistance or potential barrier than the lead terminals 11L and 11R and the wire 12, so that all of the excess dynamic charges are present. Until it completely flows out, a potential difference continues to be applied between the left and right lead terminals or both ends of the pn junction. The destruction of LSI due to static electricity occurs due to the thermal energy remaining when excess dynamic charge passes between this potential difference if it is a junction type, and due to the potential difference itself in the electric field created by the excessive dynamic charge if it is a MOS type. .
[0014]
Since the amount of the excessive dynamic charge is a charge induced by the positive electrostatic charge on the surface of the resin 10, the surface of the resin is measured by the Faraday cage or the electrostatic charge measuring device described in Japanese Patent Laid-Open No. 53-116182. It is possible to know by measuring the amount of electrostatic charge. However, the following points must be taken into account when estimating the excessive dynamic charge amount of an LSI by this method.
[0015]
The charge state of the LSI package and the relative positional relationship between the LSI and the ground, and therefore the amount of excessive dynamic charge of the lead terminal, vary greatly depending on the state placed in the manufacturing process and the inspection process or the way of handling. The field must be measured as it is. From this point, it can be said that the Faraday cage is not practically applicable to the measurement of the excessive dynamic charge amount of LSI.
[0016]
In general, the electrostatic charge on the surface of the insulator is difficult to move, and therefore the distribution is often non-uniform. In such a case, even if the total electrostatic charge amount of the LSI package is known, it is difficult to estimate the excessive dynamic charge amount for each lead terminal from the electrostatic charge amount. In such a case, it is absolutely necessary to directly measure the amount of excessive dynamic charge induced in the lead terminal. From this point of view, the electrostatic charge measuring device described in JP-A-53-116182 uses brush-type electrodes to enhance the current collection effect of the self-discharge type static eliminator used as the current collector. It is practically unusable for applications such as LSI, in which the amount of excess dynamic charge for each lead terminal with a very narrow pitch is measured.
[0017]
As is clear from the above description, in order to design the equipment and jigs of the manufacturing process or the package or chip of the LSI itself so as not to destroy the LSI, or to examine the handling method of the LSI In addition, a method and an apparatus for accurately measuring the amount of excessive dynamic charge for each lead terminal in an in-situ and in-situ state during an LSI manufacturing process are indispensable.
[0018]
In general, static electricity often has a small potential as a charge amount although the potential is high. For example, in FIG. 7B, if the value of the capacitance C1 of the device under test 1 is 1 pF and the charged amount Q1 is 10 nC, the voltage V1 with respect to the ground potential of the device under test 1 is V1 = Q1 / C1. = 10.times.10.sup.-9 / 1.times.10.sup.-12 (C / F) = 10,000V. In order to measure such an object to be measured with a very small charge and high voltage, the measurement system must fully consider that point regardless of the circuit type. That is, the charge conversion unit (the part of the measurement system that accumulates or flows the charge to be measured and converts it into voltage or current is called in this way. In the case of FIG. 7B, the dielectric 4). The impedance (that is, the reciprocal of the electrostatic capacity of the dielectric 4) must be sufficiently low so that it can be regarded as substantially zero compared to the impedance of the object to be measured. Otherwise, the entire amount of the charge to be measured is not induced / accumulated in the dielectric 4, and the amount corresponding to the capacitance value of the object to be measured remains in the object to be measured and correct measurement cannot be performed. Become. On the other hand, the measurement unit (the part of the measurement system that measures the voltage or current of the conversion unit is called in this way. In this case, the voltmeter 5) has a sufficiently high input impedance and a sufficient withstand voltage. It must be big. These are necessary in order to reliably guide all the minute charges to the converter. If the input impedance of the measurement unit is low or the internal resistance is insufficient, even a minute charge to be measured leaks to the measurement unit, resulting in a decrease in measurement accuracy.
[0019]
On the other hand, when the measurement system satisfies the above conditions, sufficient consideration must be given to the wiring system from the object to be measured to the measurement system. For example, in FIG. 7B, when a bare wire is used for the wiring 13 from the DUT 1 to the voltmeter 5, it is easy to pick up electromagnetic wave induction from the outside. The voltage due to this induction is added to the high input impedance of the voltmeter 5 to vary the voltage measurement value. On the other hand, in order to avoid the influence of electromagnetic induction, when the wiring 13 is a coaxial cable or the like, a voltage is generated in the wiring 13 due to the piezo effect generated when the cable is moved for measurement, and the measured value of the voltmeter 5 fluctuates. Resulting in.
[0020]
Such considerations for the measurement system and wiring system are generally necessary not only for measuring the excessive dynamic charge of LSI, but also for measuring the amount of electrostatic charge of very small charge and high voltage, regardless of the measurement target. It is a thing.
[0021]
Therefore, the present invention provides a method for measuring only an excessive amount of electromotive charge of an LSI lead terminal in a manufacturing process, in a state where it should be, and for each lead terminal, and a measuring apparatus used for the measurement. It is for the purpose.
[0022]
Another object of the present invention is to measure the stray capacitance between the lead terminal of the LSI and the ground using the above-described method and apparatus for measuring the excessive dynamic charge. It is an object of the present invention to provide a measuring device that obtains the amount of electrostatic energy accumulated in a lead terminal and measures the amount of electrostatic energy or charge sufficient to cause electrostatic breakdown in an LSI.
[0023]
The present invention also provides a high-accuracy charge amount measurement in a measuring device for excess dynamic charge amount and electrostatic charge amount without fluctuation of a measurement value due to deformation of a wiring from a measured object to a measurement system or electromagnetic induction. The object is to provide an apparatus.
[0024]
Further, according to the present invention, in the measuring device for excess dynamic charge amount and electrostatic charge amount, a part of the charge to be measured leaks out of the charge conversion site through the measurement unit due to the high voltage to be measured. It is an object of the present invention to provide a highly accurate measurement apparatus that prevents a decrease in measurement accuracy based on the above.
[0025]
[Means for Solving the Problems]
The charge amount measuring device of the present invention is Formed in a sharp shape at the tip of a metal bar A conductive probe; a capacitor for storing electric charge induced by the probe; a capacitor whose one electrode is set to a ground potential; and a means for measuring a voltage between the electrodes of the capacitor. The capacitor includes a charge to be measured induced by the probe. The metal rod arranged along the movement path, a metal plate provided concentrically with the metal rod and serving as the ground potential, and a dielectric interposed between the metal rod and the metal plate The pointed shape of the probe protrudes outside the metal plate. Features.
[0026]
In addition to the above-described configuration, the charge amount measuring apparatus of the present invention has a distributed capacitance structure or a parallel connection structure of a plurality of capacitors having a minute capacitance value along the movement path of the measured charge induced by the probe. Therefore, it is possible to prevent the breakdown of the voltmeter and the leakage of the measured charge due to the high voltage of the measured charge, Increasing measurement accuracy it can.
[0027]
In addition, at least, the probe, the path from the probe to the capacitor, and the capacitor are integrated so that the relative position between them is unchanged, and the integrated structure is externally connected. Therefore, the fluctuation of the measured value due to the deformation of the wiring from the object to be measured to the capacitor and the electromagnetic induction applied to the wiring can be prevented.
[0028]
Making the wiring system and measurement system fixed and integrated as described above and making the measured charge storage capacitor capacitance distributed capacity means that the measurement target is excessively induced to the lead terminal of the LSI. The measurement accuracy is improved not only when the charge is a moving charge but also when measuring the amount of a static charge whose amount is very small and generally high.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Next, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a charge amount measuring apparatus according to a first embodiment of the present invention. Referring to FIG. 1, this measuring apparatus wraps a stainless steel metal rod (length: 150 mm) 14 having a sharp tip with a dielectric 4 and further wraps the outside with a stainless steel metal plate 15. It has a pencil-shaped structure in which a probe that is close to or in contact with a measurement object, a charge storage capacitor, and wiring from the probe to the capacitor are integrated. The dielectric 4 is made of a ceramic having a thickness of 0.05 mm (relative dielectric constant: 8.5), and the capacitance value between the metal rod 14 and the metal plate 15 is 1,000 pF. In the case of LSI, even if the charge is relatively high, the amount of excess dynamic charge at the lead terminal is about several nC. The capacitance of the lead terminal is large or small depending on the package, but is approximately several pF. In order to measure the minute charge amount as described above, in this embodiment, the capacitance value of the dielectric 4 can be sufficiently increased to several hundred times the capacitance value of the lead terminal, and the impedance can be ignored. I did it. That is, the amount of charge remaining in the device under test 1 after the charge to be measured is transferred to the dielectric 4 is made so small as to be negligible with respect to the amount of charge accumulated in the dielectric 4 to improve the measurement accuracy. It was. The thickness of the outer metal plate 15 is 20 mm in diameter.
[0030]
In order to measure the excess conductive load Q of the object to be measured with this measuring apparatus, the outer metal plate 15 is set to the ground potential, and the sharp tip of the metal rod 14 is brought close to or in contact with the object to be measured, so that the excessive moving charge is generated. It is accumulated in the dielectric 4 and is obtained by Q = CV from the voltage value V between the metal rod 14 and the metal plate 15 and the capacitance value C of the dielectric 4 at that time. In rare cases, since the metal plate 15 is set to the ground potential, electromagnetic induction from the outside can be blocked. Further, since the metal rod 14 serving as both the probe and the wiring is a rigid body, there is no fluctuation in the measured value due to deformation or bending of the probe or the wiring. In the present embodiment, a ceramic having high hardness is used as the dielectric 4. However, since the outer metal plate 15 is a rigid body, the dielectric 4 does not necessarily have rigidity. Or even if it is a plastic body, a deformation | transformation and bending of wiring do not arise.
[0031]
FIG. 2 is a diagram showing an example in which the above-described measuring apparatus is applied to an LSI manufacturing process. In this example, as shown in FIG. 2A, the excessive dynamic charge of the lead terminal generated when the LSI 16 is slid on the metal rail 17 provided obliquely and conveyed from the top to the bottom is measured. Such a conveying method is a method often used in the manufacturing process of LSI. First, as shown in FIG. 1, the outermost metal plate 15 of the measuring device is connected to the ground, and the voltmeter 5 is connected between the end of the inner metal rod 14 and the ground, and then the metal rod 14 and the metal The plate 15 is short-circuited to sufficiently discharge the dielectric 4. Next, as shown in the partial enlarged view of FIG. 2B, the pointed tip of the metal rod 14 is brought into contact with the lead terminal 18 of the LSI 16 that has slid down the rail 17, and the value of the voltmeter 5 at that time is read. , Q = CV, to calculate the excess dynamic charge amount Q. The indication value of the voltmeter 5 may be displayed so that the charge amount Q can be directly read by converting the voltage value V by the capacitance value C.
[0032]
In the measuring apparatus shown in FIG. 1, the capacitor between the metal bar 14 and the metal plate 15 is connected from the contact point with the object to be measured (the sharp tip of the metal bar 14) to the input part of the voltmeter 5 (the end of the metal bar 14). Distribution capacity along the route to (part). Accordingly, during the above measurement process, the charge to be measured is transferred from the lead terminal to the metal rod 14 at a high speed on the order of picoseconds. However, the dielectric 4 has a wiring resistance corresponding to the distance from the tip of the metal rod 14. Due to the time constant difference that occurs, the batteries are charged sequentially with a time difference from the point closer to the measurement point (the tip of the metal rod 14). Therefore, even if the potential at the time of charging the lead terminal is very high, the high potential is not instantaneously applied to the voltmeter 5 and the voltmeter 5 is not destroyed. In addition, the charge to be measured is accumulated in the dielectric 4 in total without leaking to the ground through the voltmeter 5 before being accumulated in the dielectric 4. For example, assuming that the capacity of the lead terminal as the object to be measured is 1 pF and the excess dynamic charge amount is 10 nC, this lead terminal is charged to 10,000V. If there is no sequential charge in the distributed capacity manner of the dielectric 4 as described above, the voltage at the end of the metal rod 14 becomes 10,000 V at the moment when the tip of the metal rod 14 is brought into contact with the lead terminal. As a result, a voltage of 10,000 V is instantaneously applied to the voltmeter 5, and an amount of charge to be measured determined by the applied voltage and the internal resistance of the voltmeter 5 flows to the ground through the voltmeter 5. . That is, even if the destruction of the voltmeter 5 is avoided, a part of the charge to be measured is not accumulated in the dielectric 4 but leaks to the voltmeter 5 and the charge amount to be measured cannot be measured accurately.
[0033]
In the present embodiment, the structure of the dielectric 4 is made to be a distributed capacitance, but of course, as shown in FIG. 3 (a), minute capacitors with known capacitance values are connected in parallel in a lumped constant. You may comprise so that it may become a predetermined capacity value. However, in that case, it is preferable to connect the resistor r in series with each microcapacitor so that the difference in the time constant for each microcapacitor appears reliably. Alternatively, by designing the resistance value of the metal rod 14 appropriately, the resistance value along the movement path of the charge to be measured is sequentially increased by the resistance of the metal rod 14 itself, so that each minute capacitor is charged stepwise. You may be allowed to go. Furthermore, as shown in FIG. 3 (b), when a resistor R1 is provided between the end of the metal rod 14 and the voltmeter 5, the steep voltage application to the voltmeter 5 is more reliably mitigated. Damage to the voltmeter 5 and leakage of the charge to be measured can be improved. Further, as shown in FIG. 3C, the same effect can be obtained by providing the resistor R2 between the tip of the metal rod 14 and the dielectric 4. However, the resistor R2 must be integrated with the metal rod 14 and the dielectric 4 as a matter of course. In addition, in various structures so far, an amplifier circuit and an impedance conversion circuit for converting a high input impedance to a low impedance are provided in front of the voltmeter 5, and this circuit is also fixed and integrated with the metal rod 14 and the dielectric 4. In this case, fluctuations in measurement values due to electromagnetic induction to the wiring from the integrated part to the input part of the voltmeter 5 and deformation / deflection of the wiring can be eliminated, so that the measurement accuracy can be further improved.
[0034]
In the present embodiment, the metal rod 14 serves as a probe and a wiring and is composed of a single rigid body from the tip to the end. However, various methods can be used by devising the shape and structure of the tip. . For example, if an elastic thin conductor portion such as a spring metal such as phosphor bronze or a conductive rubber added with carbon is provided at the tip portion, as shown in FIG. It is possible to continuously measure the excessive dynamic charge of the lead terminal 18 of the LSI 16 that is fixed on the site and slides down the metal rail 17. Further, as shown in FIG. 5, if a plurality of cylindrical insulators 20 having a donut-shaped metal plate 19 attached to the tip are used and they are combined like a telescopic bar antenna in an automobile or a portable radio, for example. In addition to the case where the shape of the object to be measured is linear, such as an LSI lead terminal, and a small area, even when there is a certain area, the optimum contact area can be selected according to the area. . In any of the above modifications, the electric storage unit 21 for storing electric charge may have a distributed capacitance type configuration as shown in FIG. 1 as long as the capacitor and the wiring are integrated. Alternatively, a lumped constant type configuration as shown in FIGS. 3A, 3B, and 3C may be used.
[0035]
So far, when the object to be measured has a structure in which an insulator portion and a conductor portion are mixed, the case of measuring the excessive dynamic charge out of the charges induced in the conductor portion has been described. As is clear from the above description, the measurement accuracy is improved by integrating the wiring from the measured point to the dielectric and the capacitor, and the capacitor is sequentially charged with a time difference in terms of distributed capacity. The improvement in accuracy does not mean that the object to be measured is limited to excessive dynamic charges. Since the above action brings about an effect of improving the measurement accuracy in the measurement of a minute electric charge and high voltage, the present invention is applied to an apparatus for measuring the amount of electrostatic charge described in, for example, JP-A-53-116182. When applied to a measuring device having a conductive brush type self-discharge type static eliminator in the electric part, the amount of electrostatic charge charged on a measurement object having a large area can be measured more accurately. Alternatively, even if the contact portion with the object to be measured is made of a roller made of metal, conductive rubber, or conductive plastic, the same effect as that when the current collector is a brush can be obtained.
[0036]
As described above, when the charge amount measuring apparatus of the present invention is used, excessive dynamic charges that are induced to the lead terminal according to the electrostatic charge charged in the LSI package and directly cause electrostatic breakdown of the elements inside the LSI. However, if the charge amount measuring device is further provided with a DC power source and a changeover switch, the capacitance of the lead terminal with respect to the ground can be measured as described below. In addition, by using this fact, it is possible to know the electrostatic energy accumulated in the lead terminals when the LSI package is charged with static electricity. Furthermore, the energy and charge when the LSI causes electrostatic breakdown. The amount can be determined.
[0037]
FIG. 6 illustrates the present invention. Reference example It is a circuit diagram which shows a structure. Referring to FIG. Reference example Includes a DC power source 22 in addition to the charge amount measuring device. The end of the metal rod 14 of the charge storage unit 21 is connected to the ground, the DC power source 22 and the voltmeter 5 by switches 23, 24 and 25. Reference example In the method, the capacitance of the lead terminal of the LSI as the DUT 1 to the ground and the electrostatic energy accumulated in the lead terminal when the package is charged are measured by the following procedure.
[0038]
First, the switch 23 is short-circuited, and the dielectric 4 between the metal rod 14 and the metal plate 15 is discharged, so that the accumulated charge becomes zero. Then, secondly, the switch 23 is opened, and the pointed tip of the metal rod 14 is brought into contact with the DUT 1 (LSI lead terminal) and the switch 25 is short-circuited to measure the voltage VM of the dielectric 4. . As a result of the above operation, when the LSI package is charged with an electrostatic charge, the excess dynamic charge amount QL1 accumulated between the lead terminal and the ground is expressed as QL1 = CP · VM (where CP is the dielectric 4 It is obtained as known by the capacitance value of.
[0039]
Third, the switch 24 is short-circuited, and a voltage V is applied to the LSI lead terminal 1 from the end of the metal rod 14 through the tip. Thereafter, the switch 24 is opened and the tip of the metal rod 14 is separated from the lead terminal 1 to return to the initial state. Thereafter, the first and second operations are performed to measure the amount of charge QL2 accumulated in the lead terminal 1 when the lead terminal 1 is charged with the voltage value V. By this operation, the electrostatic capacitance value CL with respect to the ground of the lead terminal 1 is
CL = QL2 / V
It is obtained as
[0040]
Fourth, the capacitance value CL of the lead terminal 1 obtained by the third operation and the lead terminal 1 when the LSI package obtained by the second operation is charged with static electricity. From the accumulated excess dynamic charge amount QL1, the electrostatic energy E accumulated in the lead terminal when the package is charged,
E = (1/2) × (QL12) / CL
Calculate as
[0041]
In this way, when the LSI package is charged with static electricity during the manufacturing process, for example, the electrostatic energy accumulated in the lead terminal is obtained, and it can be determined whether or not the charging can be permitted.
[0042]
Here, in FIG. 6, if a power source having a variable output voltage is used as the DC power source 22, the third operation is sequentially performed from the lowest applied voltage V to the DUT 1 until the LSI breaks down. By repeating while changing the voltage, it is possible to obtain the charge amount at the moment when the LSI causes electrostatic breakdown, and further, the electrostatic energy.
[0043]
【The invention's effect】
As described above, according to the charge amount measuring apparatus of the present invention, when the insulator of the object to be measured including the insulator and the conductor is charged and charged with an electrostatic charge, Of the charge induced in the conductor, only the amount of excess dynamic charge can be selectively measured. Therefore, unlike the case of measuring with a conventional electrostatic charge amount measuring device such as a Faraday cage, the lead terminal excessive dynamic charge that directly causes electrostatic breakdown to the LSI can be reduced, and the static electricity charged on the package can be reduced. The measurement can be performed directly in the state where the LSI should be in the manufacturing process. In that case, the excessive dynamic charge for each lead terminal can be measured by making the probe for collecting and guiding the charge to be measured into a thin and sharp shape.
[0044]
The charge measuring device of the present invention integrates at least the probe, the path from the probe to the capacitor for charge storage to be measured, and the capacitor so that the relative position between them is unchanged, Since the integrated object has a structure in which electromagnetic shielding is applied from the outside, deformation of the wiring from the object to be measured to the capacitor and fluctuation of the measured value due to electromagnetic induction are prevented, and the measurement accuracy is high.
[0045]
Moreover, in the charge amount measuring apparatus of the present invention, the structure of the charge storage capacitor is a distributed capacitor structure or a structure in which a plurality of capacitors are connected in parallel along the movement path of the charge to be measured. And the leakage of the measured charge is prevented to improve the measurement accuracy.
[0046]
As described above, the wiring system and the measurement system are fixed and integrated, and the charge storage capacitor to be measured has a distributed capacitance. The measurement accuracy is improved not only in the case of charges, but also in the case of measuring the charge amount of electrostatic charges whose amount is very small and high voltage in general.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the structure of a charge amount measuring apparatus according to a first embodiment of the present invention.
FIGS. 2A and 2B are an external view and a partially enlarged view schematically showing a state in which the charge amount measuring apparatus according to the first embodiment of the present invention is applied to an LSI manufacturing process. FIGS.
FIG. 3 is a circuit diagram showing some of a first modification of the charge amount measuring apparatus according to the first embodiment of the present invention.
FIG. 4 is an external view showing a second modification of the charge amount measuring device according to the embodiment of the first embodiment of the present invention;
FIG. 5 is a schematic cross-sectional view showing a structure of a third modification of the charge amount measuring device according to the embodiment of the first embodiment of the present invention.
FIG. 6 shows the present invention. Reference example FIG. 6 is an equivalent circuit diagram schematically showing the configuration of
FIG. 7A is a schematic cross-sectional view of a Faraday cup as a conventional electrostatic charge measuring device. FIG. 7B is a schematic equivalent circuit diagram showing the configuration of another example of a conventional electrostatic charge amount measuring apparatus.
FIG. 8 is a model diagram for explaining excess dynamic charge in a conductor.
FIG. 9 is a model diagram for explaining the mechanism of electrostatic breakdown of an LSI due to excessive dynamic charge.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Measured object 2, 3 Metal plate 4 Dielectric 5 Voltmeter 6 Static eliminator 7 Ground surface 8 Metal piece 9 Conductor 10 Resin 11L, 11R Lead terminal 12 Wire 13 Wiring 14 Metal rod 15 Metal plate 16 LSI17 Rail 18 Lead terminal 19 Metal part 20 Insulator 21 Charge storage part 22 DC power supply 23, 24, 25 Switch

Claims (1)

A conductive probe formed in a pointed shape at the tip of a metal rod, and a capacitor with a known capacitance value in which one electrode is set to ground potential for accumulating charges induced by the probe; Means for measuring the interelectrode voltage of the capacitor, and the capacitor is provided concentrically with the metal rod disposed along the movement path of the charge to be measured induced by the probe. And a dielectric plate interposed between the metal rod and the metal plate, and the pointed shape of the probe is outside the metal plate. The charge amount measuring device is characterized by protruding .

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