JP2000269290A - Test structure and evaluation method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a test structure for accurately measuring a capacitor's capacitance at a high frequency of MHz band. SOLUTION: A resistor 1 connected to a capacitor 2 in series at evaluation of the capacitance of the capacitor 2, and a lead wire connected electrically to the resistor at the evaluation of the capacitance of the capacitor 2, are provided. Here, the resistance value of the resistor 1 is larger than the parasitic resistance value of the lead wire, while the time constant determined by the product of the resistance of the resistor 1, and the capacitance of the capacitor 2 is set smaller than the cycle of pulse voltage applied to the resistor 1, connected in series at evaluating the capacitor 2, and the capacitor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a test structure used for evaluating the capacitance of a capacitor and an evaluation method using the same.

[0002]

2. Description of the Related Art Current high performance ultra-large scale integrated circuits (ULS)
IC) operate at frequencies above 500 MHz and are expected to reach 1 GHz within the next few years. In order to achieve these high operating frequencies, close attention must be paid to the wiring scheme in LSI.

The reason is that the resistance of wiring used in ULSIC and the parasitic capacitance between wirings (line capacitance, interlayer capacitance)
However, as a whole, it acts as a parasitic effect that significantly limits the speed of the chip.

[0004] To this end, much research effort is being conducted throughout the semiconductor industry to develop processes and structures that reduce the resistance of interconnects and the parasitic capacitance between interconnects.
The development of copper interconnects and low dielectric constant dielectrics is a manifestation of two of this research effort, and as such reflects the strong demand to reduce interconnect resistance and parasitic capacitance between interconnects.

Obviously, accurate measurement of these values is becoming increasingly important given the importance of interconnect resistance and parasitic capacitance between interconnects. This is because the success of the process development ultimately depends on accurate measurements.

[0006] Measuring the capacitance of a capacitor is particularly problematic. This is because it is currently very difficult to accurately measure capacitance at high frequencies.

[0007] Tools and methods that can directly measure capacitance currently exist, but this direct measurement method is significantly affected by the presence of small parasitic inductances, such as leads present in the measurement system.

[0008] The capacitance measured in the ULSIC wiring is typically on the order of a few pF. The direct measurement method, currently using the best available equipment, is
The capacitance of these several pF can be measured only up to the frequency of 00 KHz.

Therefore, for example, almost all of the values of the dielectric constant of the interlayer insulating film which can be obtained from literatures are reported at 100 KHz or only at 200 KHz.

However, as described above, the actual U
The speed of LSIC is already approaching 1 GHz.
Current evaluation methods are not fully satisfactory because it is clearly necessary to evaluate in the frequency range actually used by ULSIC.

The reason that this method can be used even if it is not sufficiently satisfactory is that the dielectric constant of silicon dioxide, which has been widely used as a material for an interlayer insulating film, is essentially about This is because it is well known that frequencies up to 10 GHz are independent of frequency. Therefore, Equation 1
Measurements at frequencies as low as 00 KHz have been satisfactory so far.

However, a so-called low-k material having a lower dielectric constant than silicon dioxide (low-k mat).
erial) has changed the situation. These materials are generally organic and exhibit large changes in dielectric constant at certain frequencies in the MHz range.

Therefore, it is necessary to evaluate these materials at the actual operating frequency of the chip, as opposed to silicon dioxide. Therefore, there is a strong demand for a method of measuring capacitance at a high frequency in the MHz band.

[0014]

As described above, as a material having a dielectric constant lower than that of silicon dioxide, an organic substance exhibiting a large change in dielectric constant depending on a certain frequency in the MHz range has been introduced. However, the capacitance of several pF is several hundred KHz in the conventional measuring method.
Therefore, there is a problem that it is difficult to evaluate the capacitance of an organic substance having a low dielectric constant as described above.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a test structure capable of measuring a capacitance at a higher frequency than before, and an evaluation method using the same. Is to provide.

[0016]

The concept behind the approach in the present invention is to use as a test structure a resistor connected in series with the capacitance to be measured, and to dissipate the resistance in the resistor. That is, the capacitance is indirectly obtained from the energy (power loss).

That is, in order to achieve the above object, a test structure according to the present invention comprises a resistor connected in series to the capacitor when evaluating the capacitance of the capacitor, and a resistor connected in series with the capacitor when evaluating the capacitance of the capacitor. A test structure comprising a lead wire electrically connected to the resistor, wherein a resistance value of the resistor is larger than a parasitic resistance value of the lead wire, and a resistance of the resistor and a capacitance of the capacitor. The time constant determined by the product of the above is given to the resistor and the capacitor connected in series during the evaluation of the capacitor,
It is characterized in that the amplitude is smaller than the period of the signal that changes periodically with the passage of time.

Here, in order to accurately evaluate the capacitance of the capacitor, it is preferable that the time constant determined by the product of the resistance of the resistor and the capacitance of the capacitor is smaller than 10% of the period of the signal.

[0019] As the lead wires, a first lead wire for connecting the resistor to the capacitor in series, a second lead wire for connecting the resistor to the signal source of the signal, and both ends of the resistor. And a third lead wire for connecting to a voltmeter.

Further, an evaluation method according to the present invention is an evaluation method of a capacitance of a capacitor using the above test structure,
A first step of providing a signal whose amplitude varies periodically with time to a capacitor connected in series and a resistor of the test structure; and a capacitor connected in series and a resistor of the test structure. After stopping the application of the signal, a second value of the resistance of the resistor is determined.
And if the relationship between the resistance of the resistor in the test structure and the power loss is not known, a third measurement is performed to determine the relationship between the resistance of the resistor in the test structure and the power loss.
And the relationship between the resistance and the power loss of the resistor in the test structure, and the power loss value of the resistor based on the resistance value obtained in the second step, and the obtained power loss value And obtaining a capacitance value of the capacitor based on the fourth step.

Here, when performing the third step,
Performed prior to the first step, the relationship between the resistance of the resistor and the power loss may be determined, for example, by selectively passing a current through the resistor and determining the resistance of the resistor at at least one current value. It can be determined by doing.

The signal is a pulse signal. In this case, in order to accurately determine the current loss of the resistor, the measurement for determining the resistance value of the resistor of the test structure within a period shorter than the period of the pulse signal after stopping applying the pulse signal is performed. Is preferably performed.

[Operation] The test structure according to the present invention has a small time constant determined by the product of the resistance of the lead wire and the resistance of the resistor and the capacitance of the capacitor, which cause measurement errors. Therefore, when such a test structure is used, the capacitance of the capacitor at a high frequency can be accurately and easily evaluated by the test evaluation method according to the present invention.

In the evaluation method according to the present invention, since a signal is applied to the resistor and the capacitor connected in series, the energy (power loss) consumed in the resistor can be made equal to the energy stored in the capacitor. .

Here, temperature depends on the resistance of the resistor. Therefore, when a current flows through the resistor and the capacitor connected in series, the temperature of the resistor increases, and the resistance of the resistor increases. Therefore, the resistance of the resistor cannot be regarded as constant.

However, since there is a one-to-one relationship between the power loss in the resistor and the resistance of the resistor, if the relationship between the resistance of the resistor and the power loss is known, the resistance value of the resistor is determined. , The power loss value can be obtained.

Here, the relationship between the resistance of the resistor and the power loss can be easily and accurately determined by, for example, applying a DC voltage to both ends of the resistor and measuring the current flowing through the resistor and the voltage drop at the resistor. You can ask.

Therefore, after giving a signal to the resistor and the capacitor connected in series, the resistance value is obtained by measuring the current flowing through the resistor and the voltage drop at both ends of the resistor.
The power loss of the resistor can be obtained from the relationship between the obtained resistance value and the relationship between the resistance of the resistor and the power loss.

The power loss is equal to the energy stored in the capacitor as described above, and the energy stored in the capacitor is a function of voltage and capacitance. The power loss value can be determined as described above, and the voltage is known in advance by the applied signal. That is, since values other than the capacitance value of the capacitor are known, the capacitance value of the capacitor can be obtained by calculation.

Therefore, according to the evaluation method of the present invention, the capacitance value of the capacitor can be determined based on the measurement result of the current flowing through the resistor and the voltage drop at the resistor, which can be accurately measured even at a high frequency. Since it can be obtained, the capacitance of the capacitor at a high frequency can be accurately obtained.

[0031]

Embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is an equivalent circuit showing a capacitance measuring system according to one embodiment of the present invention.

This evaluation system is roughly divided into a resistor 1, a pulse power supply 3 for applying a pulse voltage to a resistor 1 and a capacitor 2 connected in series, and a resistor 1.
Current and voltage measuring means for measuring the current flowing through the resistor and the voltage drop in the resistor 1, and a lead wire electrically connected to the resistor 1 when measuring the current and the voltage drop. ing.

The resistor 1 and the lead constitute a test structure. The lead wire is used to connect the resistor 1 to the ammeter 11, to connect the resistor 1 to the DC power supply 10, and to connect the resistor 1 to the voltmeter 12 at both ends of the resistor 1. For connecting the body 1 and the capacitor 2 and the like.

In order to increase the accuracy of measuring the current flowing through the resistor 1 and the voltage drop at the resistor 1, the resistance of the resistor 1 is set sufficiently larger than the resistance parasitic value of the lead wire.

Further, when a pulse voltage is applied to the resistor 1 and the capacitor 2 connected in series, the resistance of the resistor 1 and the capacitance of the capacitor 2 are set so that the charging and discharging of the capacitor 2 can be completed. Is set to 10% or less of the period of the pulse voltage generated by the pulse power supply 3. By setting such a value, the resistor 1
And the energy stored in the capacitor 2 can be made equal.

A resistor 1 and a capacitor 2 connected in series
When a pulse voltage is applied to the first and second switches, the first switch 4 is opened, the second switch 5 is closed, and the third to sixth switches 6 to 9 are opened.

The current / voltage measuring means includes a DC power supply 10 and
It is composed of an ammeter 11 and a voltmeter 12. When measuring the resistance value of the resistor 1, the first switch 4 is closed, the second switch 5 is opened, the third and fourth switches 6, 7 are closed, and the fifth and sixth switches are closed. Switches 8 and 9 are closed. As a result, the DC power supply 10 and the ammeter 11 are connected in series, and the voltmeter 12 and the resistor 1 are connected in parallel. The resistance value of the resistor 1 is obtained from the current value measured by the ammeter 11 and the voltage value measured by the voltmeter 12.

Each of the resistor 1 and the capacitor 6 is formed of a wiring formed by a process well known in the art.

As the resistor 1, for example, as shown in the plan view of FIG.

On the other hand, the capacitor 2, for example, as shown in the plan view of FIG. 3 (a), the wiring 2 _1, 2 ₂ of the comb-shaped pattern pair formed so as to mesh with each other,
These lines 2 _1, 2 ₂ and those constructed from an insulating film formed 2 ₃ Prefecture between, or, as shown in the sectional view of FIG. 3 (b), 1 pair of wires formed on the upper and lower ₄ , ₂₅ ,
Those of the wiring 2 _4, 2 ₅ configured plate structure from the formed insulating film 2 ₆ which between the like.

The capacitor 2 having the structure shown in FIG.
Is commonly used in this field to measure the capacitance between wires in the same layer. On the other hand, FIG.
The capacitor 2 having the structure shown in FIG. 2B is used to measure the capacitance between wirings in different layers.

Next, a description will be given of a method for measuring capacitance using the evaluation system configured as described above. FIG. 4 is a schematic diagram showing the measuring method, and FIG. 5 is a flowchart showing the measuring method.

First, as shown in FIG. 4A, the switches 4 to 9 are opened and closed, a DC power supply 10 is connected to both ends of the resistor 1, and a direct current is selectively supplied to the resistor 1. In this state, the current flowing through the resistor 1 and the voltage drop at both ends of the resistor 1 are measured by the ammeter 11 and the voltmeter 12, respectively. At this time, since the plate (wiring) of the capacitor 2 is maintained at the same voltage throughout this measurement, the capacitor 2 is substantially short-circuited.

Based on the above measurement results, the resistance value of the resistor 1 and the power loss value in the resistor 1 are obtained by calculation. The resistance value of the resistor 1 can be easily obtained by dividing the voltage drop across the resistor 1 by the current. On the other hand, the power loss value of the resistor 1 can be easily obtained from the product of the measured current and the voltage drop.

By performing such a process at least once, the relationship between the resistance of the resistor 1 and the power loss is obtained (step S1).

Here, in order to obtain an accurate relationship, D
It is preferable to obtain the power loss value at a plurality of different resistance values by changing the voltage of the C power supply 10. However, even if a single resistance value and the power loss value are used, if the resistance value is zero, the power loss value is obtained. Is also 0, the relationship between the resistance value and the power loss value can be obtained.

In this way, a quantitative relationship between the resistance and the power loss can be obtained as shown in FIG. In the figure, points indicate the resistance value and the power loss value obtained from the measurement results.

In step S1, the scale of the resistance value of the resistor 1 is calibrated against the power loss value. The purpose of this scale calibration is to establish a relationship between the resistance of the resistor 1 and the power loss. If power is consumed in any resistor 1, the temperature of the resistor 1 rises.

If the resistor 1 is formed of metal wiring,
A rise in the temperature of the resistor 1 increases the resistivity of the metal. The increase in resistivity is determined by the temperature coefficient of resistivity, which is a property of the metal itself.

[0051] Increasing the resistivity increases the resistance, which slightly increases the power loss value, and finally, an equilibrium is established where the resistance reflects the elevated temperature or power loss value. This phenomenon is well understood qualitatively.

Incidentally, the actual relationship between the resistance value and the power loss value depends on the actual pattern of the resistor 1 used and the process used for manufacturing the same. This is because the temperature rise due to a constant power loss value is a function of the actual resistor 1 pattern. Therefore, even though the increase in resistivity is determined by the temperature coefficient of resistivity, it is difficult to analytically determine the relationship between the resistance value and the power loss value.

Thus, the purpose of step S1 is to determine the relationship between resistance and power dissipation for the particular resistor 1 (test structure) actually used.

Next, as shown in FIG. 4C, by opening and closing the switches 3 to 9, the resistor 1, the capacitor 2, and the pulse power source 3 are connected in series, and the resistors connected in series are connected. A pulse voltage is applied to the body 1 and the capacitor 2 (Step S2). In step S2, it is important that the pulse voltage is continuously applied for a period necessary for stabilizing the resistance of the resistor 1, for example, about 10 minutes.

The reason why the pulse voltage is used is that the pulse voltage most accurately reproduces the actual signal in the ULSIC, and furthermore, the capacitor in the state where the state when the ULSIC is actually used is accurately reproduced. This is because it is desirable to evaluate the capacity of No. 2.

Instead of the pulse voltage, another voltage whose amplitude periodically changes over time, for example, an AC voltage whose amplitude changes like a sine wave over time may be used. The frequency of the AC voltage is the desired frequency f
Is set within the range of the ULSIC maximum operating frequency.

The measuring method of this embodiment differs from the conventional direct measuring method in that the frequency of the current flowing through the capacitor 2 can be the same as the actual operating frequency of the ULSIC. The reason is that in the measurement method of the present embodiment,
This is because the capacitance of the capacitor 2 is indirectly measured based on the resistance value of the resistor 1 having no frequency dependence. A specific range of the frequency is, for example, a range of 1 MHz to 10 GHz. Of course, the measurement may be performed at a lower frequency if desired, but there is no reason to do so.

A resistor 1 and a capacitor 2 connected in series
Resistor 1 generated by applying a pulse voltage to
Is given by C · V ² · f / 2. Here, C is the capacity of the capacitor 2, V is the peak voltage of the pulse voltage, and f is the reciprocal (frequency) of the cycle of the pulse voltage.

Therefore, in this step S2, an amount of power essentially determined completely by the capacitance (C) of the capacitor 2 to be evaluated and other known amounts (V, f) is stored in the resistor 1. Will be lost.

Next, as shown in FIG.
1, a DC current is applied to the resistor 1 and the current value and the voltage value of the resistor 1 obtained by the measurement are used to determine the value of the resistor 1
Is determined (step S3).

However, in step S3, compared with the case of step S1, a DC current is applied to the resistor 1 for a very short period, and the current and the voltage are measured. This is because, if a DC current flows for a long period of time, the resistance value of the resistor 1 will be different from that immediately after the application of the pulse voltage is stopped.

For the same reason, the resistor 1 is not cooled between the time when the application of the pulse voltage is stopped and the measurement. Switching from step S2 to step S3 manually by a connection configuration requiring several tens of seconds is not allowed even if it is not several minutes. Therefore, step S
Switching from step 2 to step S3 is automatically executed under electronic control and program control.

Finally, as shown in FIG. 4E, the resistance value of the resistor 1 obtained in step S3 is
Using the relationship between resistance and power loss established in 1
The power loss value of the resistor 1 during the period of step S2 is obtained, and the obtained power loss value is obtained by the following equation: power = CV
Based on the ² f / 2, determining the capacitance C of the capacitor 2 (step S4).

As described above, the measuring method according to the present embodiment measures the capacitance indirectly by determining the power loss value of the resistor 1 connected in series to the capacitor 2, and the actual measurement to be performed is DC. Only the measurement of the current and voltage of the resistor 1 under the conditions is performed.

Therefore, the measuring method of the present embodiment does not have the problem of measuring at a high frequency which exists in the conventional measuring method, and evaluates a small capacitance at a high frequency within the operating frequency range of the capacitor and the chip. it can. Specifically, it becomes possible to measure a capacitance of about several pF at a frequency exceeding 1 MHz.

The only restriction imposed on the measuring method according to the present embodiment relates to the resistance of the resistor 1. Resistor 1
Must be higher than the parasitic resistance of the lead wire or the like.

At the same time, the resistance of the resistor 1 is set so that the time constant of the circuit, which is given by the product of the resistance of the resistor 1 and the capacitance of the capacitor 2, becomes much smaller than the period of the pulse voltage used for measurement. Must be small enough.

As described above, this is for ensuring complete charging and discharging of the capacitor 2 in each cycle of the pulse voltage. A resistor 1 having a resistance value in the range of 10 to 200Ω is sufficient in most cases.
The structure can be easily manufactured as shown in FIG.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the resistor 1
The relationship between the resistance and the power loss was determined (step S1).
If these relationships are known in advance, step S
Step 1 can be skipped and the process can proceed to step S2.

Since the relationship between the resistance of the resistor 1 and the power loss is necessary in step S4, the step S1 for obtaining the relationship between the resistance of the resistor 1 and the power loss is not always necessary first.

In addition, various modifications can be made without departing from the spirit of the present invention.

[0072]

As described above in detail, according to the present invention, the resistance of the resistor can be easily measured by using a test structure including a lead wire and a resistor having a small parasitic resistance and a small time constant which causes a measurement error. And the voltage drop measurement results,
Measuring the capacitance indirectly allows the capacitance at high frequencies to be accurately and easily evaluated.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit showing a capacitance measuring system according to an embodiment of the present invention.

FIG. 2 is a plan view showing a specific configuration of a resistor.

FIG. 3 is a plan view and a cross-sectional view showing a specific configuration of a resistor.

FIG. 4 is a schematic diagram showing a capacitance measuring method according to an embodiment of the present invention.

FIG. 5 is a flowchart showing a method for measuring the capacitance.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Resistor 2 ... Capacitor 3 ... Pulse power supply 4-9 ... Switch 10 ... DC power supply 11 ... Ammeter 12 ... Voltmeter S1 ... Step of obtaining the relationship between resistance of a resistor and power loss S2 ... Connected in series Step of applying a pulse voltage to the resistor and the capacitor S3: Step of determining the resistance value of the resistor immediately after stopping application of the pulse voltage S4: Step of determining the capacitance of the capacitor

Claims (6)

[Claims] 1. A test structure comprising a resistor connected in series with the capacitor when evaluating the capacitance of the capacitor, and a lead wire electrically connected to the resistor when evaluating the capacitance of the capacitor. Wherein the resistance value of the resistor is larger than the parasitic resistance value of the lead wire, and the time constant determined by the product of the resistance of the resistor and the capacitance of the capacitor is: A test structure, wherein an amplitude applied to the resistor and the capacitor connected in series is smaller than a period of a signal whose amplitude periodically changes over time. 2. The test structure according to claim 1, wherein said time constant is smaller than 10% of a period of said signal. 3. A lead wire for connecting the resistor to the capacitor in series, and a second lead wire for connecting the resistor to a signal source of the signal. A third terminal for connecting both ends of the resistor to a voltmeter.
The test structure according to claim 1, further comprising: 4. A method for evaluating the capacitance of a capacitor using the test structure according to claim 1, wherein an amplitude is applied to the capacitor connected in series and the resistor of the test structure. Providing a signal that changes periodically with the passage of time; and stopping applying the signal to the series-connected capacitor and the resistor of the test structure. A second step of determining a resistance value; and, if the relationship between the resistance of the resistor of the test structure and the power loss is not known, performing a measurement to determine the relationship between the resistance of the resistor of the test structure and the power loss. A third step of obtaining, a power loss value of the resistor based on a relationship between a resistance of the resistor of the test structure and a power loss, and a resistance value obtained in the second step; loss Obtaining a capacitance value of the capacitor based on the value. 5. The method according to claim 1, wherein the third step is performed before the first step, and selectively supplies a current to the resistor.
The relationship between the resistance of the resistor and the power loss is determined by performing a measurement for determining the resistance of the resistor at at least one current value.
4. The method for evaluating a capacitor according to item 1. 6. The signal is a pulse signal, and after stopping applying the pulse current to the resistor and the capacitor, within a period shorter than a cycle of the pulse signal,
The method for evaluating a capacitor according to claim 4, wherein a measurement is performed to determine a resistance value of the resistor of the test structure.