JP2005207926A - Method and instrument for measuring resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an instrument for measuring a resistance capable of measuring properly an effective resistance value of a conductive member in discharge of an electric charge charged in a protection object protected from static electricity. <P>SOLUTION: A prescribed capacity of capacitor 204 is connected between an electrode 100 and a prescribed node (grounding). The electrode 100 is fixed onto an instrument body. The instrument main body is provided with a surface electrometer 201, an arithmetic processing part 202, a display part 203, the capacitor 204, a voltage source 205, and a switch 206. The switch 206 is closed and the capacitor 204 is charged preliminarily by the voltage source 205, when measuring the resistance of the measured object. Then, the switch 206 is opened, and the electrode 100 is brought into contact with the measuring object to discharge the capacitor 204. A voltage of the electrode 100 is measured therein by the surface electrometer 201. A time constant of the measured object is acquired based on a voltage measured result therein, and the time constant is converted into the resistance value of the measured object to be output. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a resistance measuring apparatus and method for measuring the resistance of a conductive member used to protect an electronic component such as a semiconductor device from static electricity.

Since a semiconductor device manufactured using microfabrication technology is easily damaged by static electricity, a conductive member having a resistance value of about 1 kΩ to 10 ¹⁴ Ω is statically protected from static electricity at the manufacturing site. Used as an electrical protection member. Specifically, the conductive member for electrostatic protection stores the tip of tweezers used for handling the semiconductor device, the floor surface of the work place, the upper surface of the work table on which the semiconductor device is placed, and the semiconductor device. It is used for trays, packing materials, finger sack, wristbands for removing static electricity, and shoe soles of work shoes (see Patent Document 1 and Patent Document 2).

By the way, if the resistance value of the conductive member described above is too low, the electric charge charged on the semiconductor device to be protected is instantaneously discharged, so that an excessive discharge current is generated and damages the protection target. For this reason, it is necessary to set the resistance value of the conductive member to an appropriate value of about 1 kΩ to 10 ¹⁴ Ω as described above in order to suppress the discharge current due to the charge charged on the object to be protected and prevent charging. A means for measuring and evaluating the resistance value is required.

  A conventional method for measuring the resistance value of the conductive member will be described with reference to FIG. The example shown in the figure shows a case where the resistance of the conductive mat 1000 placed on the floor surface of the work place is measured. The conductive mat 1000 of the object to be measured is placed on the metal plate 110 and this mat 1000 is shown. An electrode 1300 weighing about 2 kilograms is placed on the substrate. An ohmmeter 1200 is connected between the electrode 1300 and the metal plate 1100.

The weight of the electrode 1300 represents the weight of the worker applied to the conductive mat 1000. The greater the load applied to the conductive member by the electrode 1300, the smaller the resistance value obtained as a measurement value. Show the trend. For this reason, the weight of the electrode 1300 is set to be smaller than the actual load by the human body, and is generally set to about 2 kilograms in anticipation of safety against static electricity. According to this prior art, the resistance value of the mat 1000 is measured by the resistance meter 1200 in a state where a load of about 2 kilograms is applied to the mat 1000.
JP-A-9-143279 JP-A-8-204376

  However, according to the resistance value measuring method according to the conventional method described above, when the protection target placed on the conductive member is a semiconductor device or the like, the contact area between the conductive member and the protection target is small. It is extremely small and the load applied to the conductive member by the object to be protected is small. For this reason, there is a problem that the electric charge charged on the object to be protected is not discharged through the conductive member, and therefore the resistance value of the conductive member cannot be measured.

  The present invention has been made in view of the above circumstances, and discharge of electric charges charged on an object to be protected without being affected by the contact area or load between the object to be protected and the conductive member to be protected from static electricity. An object of the present invention is to provide a resistance measuring apparatus and method capable of appropriately measuring the effective resistance value of a conductive member against the above.

In order to solve the above problems, the present invention has the following configuration.
That is, the resistance measuring apparatus according to the present invention includes an electrode that is in contact with an object to be measured, a capacitive element connected between the electrode and a predetermined node, and an arbitrary element that is higher than a test standard. Charging means for charging to the voltage of the electrode, voltage measuring means for measuring the voltage of the electrode when the capacitive element is discharged when the electrode is in contact with the object to be measured, and measurement by the voltage measuring means Time constant acquisition means for acquiring a time constant of the object to be measured based on a result, and resistance value conversion means for converting the time constant into a resistance value of the object to be measured.

  In the resistance measurement device, for example, the time constant acquisition unit may be configured such that the voltage measured by the voltage measurement unit obtains a predetermined coefficient that defines the time constant from a predetermined first voltage according to the test standard. The time until the second voltage obtained by multiplying by one voltage is measured, and the time is output as the time constant.

In the resistance measuring apparatus, for example, the voltage measuring means is a surface potentiometer.
In the resistance measurement device, for example, the electrode has a shape corresponding to a device to which the measurement object is applied as an electrostatic protection member.
Further, the resistance measuring device further includes, for example, load measuring means for measuring a load applied to the electrode.

  In the resistance measuring method according to the present invention, (a) a predetermined capacitive element connected to an electrode to be brought into contact with an object to be measured at the time of measurement is charged in advance to an arbitrary voltage higher than the test standard. A charging step; (b) a discharging step in which the capacitive element connected to the electrode is discharged by bringing the electrode into contact with the object to be measured; and (c) when the capacitive element is discharged. A voltage measurement step for measuring the voltage of the electrode; (d) a time constant acquisition step for acquiring a time constant of the object to be measured based on a voltage measurement result of the electrode; and (e) a time constant of the measurement target. And a resistance value conversion step for converting into the resistance value of the object.

  In the resistance measurement method, for example, in the time constant acquisition step, the voltage measured in the voltage measurement step is a predetermined coefficient that defines the time constant from a predetermined first voltage according to the test standard. The time until the second voltage obtained by multiplying the first voltage is measured, and the time is output as the time constant.

  According to the present invention, the effective resistance value of the conductive member against the discharge of the electric charge charged on the protection target without being affected by the contact area or load between the protection target and the conductive member to be protected from static electricity. Can be measured appropriately.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing an overview of a resistance measuring apparatus 1 according to the present embodiment. As shown in the figure, the resistance measuring apparatus 1 is composed of an electrode 100 to be brought into contact with an object to be measured (not shown) at the time of measurement, and an apparatus main body 200. It is fixed to the apparatus main body 200 in an insulated state.

  FIG. 2 shows the configuration of the resistance measuring apparatus. Among the components shown in the figure, the surface electrometer 201, the arithmetic processing unit 202, the display unit 203, the capacitor (capacitive element) 204, the voltage source 205, and the switch 206 are housed in the apparatus main body 200 described above. The capacitance value of the capacitor 204 is switchable (variable) and can be selected from a plurality of predetermined capacitance values. As will be described later, this capacitance value has the meaning of determining the measurement range of the resistance value.

  Here, the capacitor 204 is connected between the electrode 100 and the case (predetermined node) of the grounded apparatus main body 200. That is, the capacitor 204 forms a capacitor circuit in which one end is set to the ground potential (ground potential) and the other end is connected to the electrode 100. In addition, a series circuit including a voltage source 205 and a switch 206 is connected between the electrode 100 and the ground as a charging means for charging the capacitor 204 to a predetermined voltage higher than the test standard. Connected in parallel.

  Further, a surface electrometer 201 is provided in the apparatus main body 200 as a voltage measuring means so as to face the surface of the electrode 100. A signal indicating the measurement result of the surface electrometer 201 is given to the calculation processing unit 202 that executes the calculation process of the resistance value, and a signal showing the calculation result of the calculation processing unit 202 is given to the display unit 203. Although not particularly illustrated, a power supply circuit for each of the surface electrometer 201, the arithmetic processing unit 202, and the display unit 203 is also built in the apparatus main body 200.

Next, the operation of this embodiment will be described.
At the time of measurement, first, the switch 206 is closed by an operator's operation, and a predetermined voltage Vint higher than the test standard is applied between the ground and the electrode 100 by the voltage source 205. As a result, the capacitor 204 connected to the electrode 100 is charged to the voltage Vint in advance. When the capacitor 204 is charged to the voltage Vint, the surface electrometer 201 detects this, and the arithmetic processing unit 202 controls the switch 206 to be opened. As a result, the capacitor 204 is maintained in a state of being charged to the voltage Vint, and the electrode 100 is charged to the electric charge stored in the capacitor 206.

  Subsequently, an operator brings the electrode 100 into contact with a measurement target (not shown). Here, the object to be measured is, for example, a conductive object (mat, electronic device tray, packing material, etc.) whose one surface is in contact with the ground surface, and a resistance R (not shown) of the amount to be measured. Have. When the electrode 100 is brought into contact with the object to be measured, the charge stored in the capacitor 204 connected to the electrode 100 is discharged through the object to be measured, and the charge of the capacitor 204 charged to the voltage Vint is measured. As shown by a dotted line in FIG. 3, the voltage V of the electrode 100 decreases exponentially with the passage of time and approaches zero (ground potential).

At this time, the voltage V applied to the object to be measured is indicated by a solid line in FIG. 3 and is expressed by the following equation (1).
V = V1 × exp (-t / CR) (1)
In the above equation (1), C is the capacitance of the capacitor 204, and R is the resistance of the object to be measured. These products CR are called time constants and are represented by τ. V1 is the discharge peak voltage, and t is time.

The surface potential meter 201 constantly measures the surface potential of the electrode 100 and outputs the measurement result to the arithmetic processing unit 202 including a timer circuit.
When the measurement processing unit 202 inputs the measurement result from the surface electrometer 201, the calculation processing unit 202 calculates the resistance R of the object to be measured based on the measurement result as follows. That is, the arithmetic processing unit 202 acquires the time constant τ of the measurement target object from the measurement result of the surface electrometer 201 and converts the acquired time constant into the resistance R of the measurement target object.

  Here, a method for obtaining the time constant τ will be described with reference to FIG. In the figure, a solid line indicates a voltage waveform generated in the object to be measured as a discharge current flows through the object to be measured, and a broken line indicates a discharge voltage waveform of the capacitor 204. As shown in the figure, when the electrode 100 is brought into contact with the object to be measured at time t0, the capacitor 204 is thereby discharged, and the terminal voltage thereof gradually decreases. On the other hand, the discharge current of the capacitor 204 flows through the resistance R of the object to be measured, and a voltage that gradually decreases with the discharge peak voltage V1 as a peak value is generated in the object to be measured. This discharge peak voltage V1 corresponds to the test standard, and is, for example, 1000V. That is, the above-mentioned charging voltage Vint (that is, the voltage of the voltage source 205) is appropriately set so that the discharge peak voltage V1 becomes a predetermined value determined by the test standard.

The voltage waveform indicated by the solid line in FIG. 3 corresponds to the time constant τ of the object to be measured.
Here, if t = CR and the voltage V at that time is V2, the following equation (2) is obtained from the above equation (1). Where e is the base of the natural logarithm.
V2 = V1 / e (2)
The time constant τ (= CR) of the measurement object is measured as an elapsed time from the time t1 when the discharge peak voltage V1 is measured to the time t2 when the voltage V2 of the above equation (2) is measured. From the above equation (2), the voltage V2 is obtained by multiplying the discharge peak voltage V1 by the reciprocal of the base e of the natural logarithm (predetermined coefficient = about 0.37), and has a value of about 37 percent of the discharge peak voltage V1. Become.

The arithmetic processing unit 202 calculates the resistance R of the measurement object from the time constant τ acquired as described above. That is, the resistance R is calculated from τ / C.
As an example, when the capacitance value C of the capacitor 204 is 0.1 pF and the time constant τ is measured for 0.1 seconds, 1 M ohm is obtained as the resistance R.

  In the present embodiment, since the surface electrometer 201 is used, the lower limit of the measured value depends on the operating frequency of the surface electrometer 201. That is, the surface electrometer 201 takes in the electric lines of force from the electrode 100 through the gate that opens and closes at a frequency of about 500 to 1000 times per second, and detects the potential from the voltage waveform induced at that time. Yes. For this reason, when the value of the time constant τ of the voltage waveform indicated by the solid line in FIG. 3 decreases, the measurement accuracy of the constant number τ by the surface electrometer 201 decreases.

  On the other hand, the upper limit of the measured value depends on the time during which the operator maintains the state in which the electrode 100 is in contact with the object to be measured. That is, the upper limit of the time constant τ is improved as the electrode 100 is kept in contact with the object to be measured, and thus the upper limit of the measured value is improved. However, since the working time is limited, for example, if the upper limit of the time constant τ is limited to 100 seconds, the resistance value R can be measured up to 1 GΩ (when C = 0.1 pF).

  Further, if the capacitance value C of the capacitor 204 is changed, the resistance value R for the same time constant τ is different, so that the capacitance value C of the capacitor 204 can be used as a parameter for switching the measurement range. That is, even if the time constant τ is limited to a certain range for measurement accuracy reasons based on the frequency characteristics of the surface potential meter 201, the display range of the resistance value R can be switched by switching the capacitance value C of the capacitor 204. As a result, the measurement range of the resistance value R can be improved regardless of the restriction on the frequency characteristics of the surface electrometer 201.

As an example, the measurable range of the resistance value R with respect to the capacitance value C and the time constant τ is shown.
When C = 10 μF and τ = 0.01 to 99 seconds, R = 103 to 10 ⁷ Ω.
When C = 0.1 μF and τ = 0.01 to 99 seconds, R = 105 to 10 ⁹ Ω.
When C = 1000 pF and τ = 0.01 to 99 seconds, R = 107 to 10 ¹¹ Ω.
That is, as understood from this example, even if the measurement range of the time constant τ is fixed to 0.01 to 99 seconds, the measurement range of the resistance value R can be arbitrarily set by switching the capacitance value C of the capacitor 204. Can be changed. Therefore, the measurement range of the resistance value R can be expanded without being restricted by the frequency characteristics of the surface electrometer 201.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and design changes and the like within a scope not departing from the gist of the present invention are also included in the present invention. For example, in the above-described embodiment, the surface potentiometer 201 is used as the voltage measuring unit, but a normal voltmeter may be used. However, when a normal voltmeter is used, there is a disadvantage that the upper limit of the measurement voltage is limited for safety reasons against high voltages. On the other hand, since the surface electrometer 201 is used in the above-described embodiment, the above-described disadvantages when a normal voltmeter is used can be avoided, and the upper limit of the measurement voltage can be greatly expanded. .

  In the above-described embodiment, the shape of the electrode 100 is not particularly limited. However, this shape is assumed to have a shape corresponding to a device to which the measurement target is applied as an electrostatic protection member. Thus, it is possible to perform an approximate measurement when using a device that is actually a protection target, and to further improve the measurement accuracy. Specific examples of the shape of the electrode 100 include the same shape, needle shape, spherical shape, and plate shape as the lead terminal of the package in which the semiconductor chip to be electrostatically protected by the object to be measured is sealed.

  Furthermore, it is good also as a thing further provided with the load measurement means which measures the load applied to this electrode 100, when the electrode 100 contact | abuts to a to-be-measured object. As a result, the discharge can be appropriately reproduced taking the load into consideration, and the resistance value of the object to be measured can be measured with higher accuracy.

It is a perspective view showing roughly an outline of a resistance measuring device concerning an embodiment of the present invention. It is a block diagram which shows the structure of the resistance measuring apparatus which concerns on embodiment of this invention. It is a wave form diagram for demonstrating the principle of operation of the resistance measuring apparatus which concerns on embodiment of this invention. It is explanatory drawing for demonstrating the resistance measuring method which concerns on a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100; Electrode, 200; Apparatus main body, 201; Surface electrometer, 202; Arithmetic processing part, 203; Display part, 204; Capacitor, 205; Voltage source, 206;

Claims (7)

An electrode in contact with an object to be measured;
A capacitive element connected between the electrode and a predetermined node;
Charging means for charging the capacitive element to an arbitrary voltage higher than a test standard;
Voltage measuring means for measuring a voltage of the electrode when the capacitive element is discharged by contacting the electrode with an object to be measured;
Time constant obtaining means for obtaining a time constant of the object to be measured based on a measurement result of the voltage measuring means;
Resistance value conversion means for converting the time constant into a resistance value of the object to be measured;
A resistance measuring device. The time constant acquisition means includes
Until the voltage measured by the voltage measuring means changes from a predetermined first voltage according to the test standard to a second voltage obtained by multiplying the first voltage by a predetermined coefficient that defines the time constant. 2. The resistance value measuring apparatus according to claim 1, wherein time is measured and the time is output as the time constant.   The resistance value measuring apparatus according to claim 1, wherein the voltage measuring unit is a surface potentiometer.   The resistance measuring device according to any one of claims 1 to 3, wherein the electrode has a shape corresponding to a device to which the object to be measured is applied as an electrostatic protection member.   5. The resistance value measuring apparatus according to claim 1, further comprising a load measuring unit that measures a load applied to the electrode. (A) a charging step of precharging a predetermined capacitive element connected to an electrode to be brought into contact with an object to be measured at the time of measurement to an arbitrary voltage higher than a test standard;
(B) a discharging step of discharging the capacitive element connected to the electrode by bringing the electrode into contact with the object to be measured;
(C) a voltage measuring step for measuring a voltage of the electrode when the capacitive element is discharged;
(D) a time constant acquisition step of acquiring a time constant of the object to be measured based on a voltage measurement result of the electrode;
(E) a resistance value conversion step for converting the time constant into a resistance value of the object to be measured;
A resistance measurement method including: In the time constant acquisition step,
Until the voltage measured in the voltage measurement step changes from a predetermined first voltage according to the test standard to a second voltage obtained by multiplying the first voltage by a predetermined coefficient that defines the time constant. 7. The resistance value measuring method according to claim 6, wherein time is measured and the time is output as the time constant.

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