JP3235272B2 - Wiring evaluation method and evaluation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for evaluating wiring, and more particularly to an apparatus for estimating the life of aluminum wiring laid on a semiconductor wafer.

[0002]

2. Description of the Related Art Electromigration (hereinafter, referred to as EM) life of an Al wiring is conventionally estimated by assembling a package and then applying a constant current for a long time at a constant temperature in a constant temperature bath. １０００1000 hr was required. Proceedings of the 38th Annual Conference of the Japan Society of Applied Physics No. 2 (1991), page 639,
A method for evaluating the activation energy of aluminum wiring in a short time has been proposed.

In this evaluation method, a large number of samples each having a wiring pattern under test having different heat radiation characteristics are supplied with current at a constant current density Jc, and each sample is subjected to heat conduction.
The wiring temperature is calculated based on the simulation (three-dimensional heat radiation characteristic analysis) and the temperature coefficient of resistance, and the disconnection time of each sample is measured to obtain the relationship between the wiring temperature and the disconnection time for each sample. A characteristic line indicating the relationship between the wiring temperature and the disconnection time in the wiring pattern under test is obtained, and the activation energy Ea is estimated from the slope ratio.

Therefore, EM life (mean time to failure MT
F) is a function value of the current density J, the wiring temperature T, and the activation energy Ea. Therefore, if the activation energy Ea calculated by the above-described evaluation method is used, a desired wiring temperature (for example, 150 ° C.) is used. ) can be estimated EM lifetime in further if it is known the relationship between the wiring temperature T and current density J by the heat conducting simulations, EM lifetime at any current density J can be estimated.

[0005]

However, in the evaluation method proposed above, it is necessary to change the heat radiation characteristics for each sample.
For this purpose, heat radiation fins having different shapes are provided on a part of each aluminum wiring under test, thereby changing the heat radiation characteristics and changing the wiring temperature T. However, according to the wiring temperature change method, it is necessary to calculate each wire temperature by carrying out heat-conducting simula- Reshi <br/> ® emission (3D radiation characteristic analysis) for each sample, as a result, not must not execute the creation and their heat conduction simulation each sample, it has been a great deal of work burden.

In addition, such a change in the shape of the radiating fins has a limit on a change in the obtained wiring temperature, and as a result, the accuracy of the obtained characteristic line gradient, that is, the activation energy Ea is reduced. . The present invention has been made in view of the above problems, and an object of the present invention is to provide a wiring evaluation method and an evaluation apparatus which can reduce the work load and obtain highly accurate EM life / wiring temperature characteristics.

[0007]

According to the present invention, there is provided a method for evaluating a wiring, wherein a test object having the wiring laid on an insulator is maintained at a plurality of predetermined temperature states and the current is applied to the wiring at a constant current density. br /> energized the constant current, the measured resistance values and the disconnection time of the wiring for each temperature condition, of the respective wires based on the resistance temperature coefficient of said wires as measured resistance values and previously The method is characterized in that a temperature is calculated and a relationship between each of the disconnection times and the temperature of each of the wirings is determined.

As shown in the conceptual diagram of FIG. 7, the wiring evaluation apparatus of the present invention comprises a temperature maintaining means for maintaining a test object having a wiring laid on an insulator at a plurality of predetermined temperature states;
Energizing means for applying a constant current to the wiring at a constant current density ; measuring means for measuring each resistance value and each disconnection time of the wiring for each of the temperature conditions; and each of the resistance values and the previously measured wiring Wiring temperature calculating means for calculating the temperature of each of the wirings based on the temperature coefficient of resistance of the wiring; and disconnection of the wiring at an arbitrary wiring temperature based on a relationship between each of the wiring temperatures and each of the disconnection times. Evaluation means for estimating time or activation energy.

As the wiring, various conductor materials used for electric wiring, such as aluminum and aluminum alloy, are employed.

[0010]

According to the present invention, the resistance value and the disconnection time H are measured by changing the ambient temperature of the sample while energizing the metal wiring having a predetermined shape at a constant current density Jc. Next, each wiring temperature T is calculated from the previously measured resistance temperature coefficient of the metal wiring and the resistance value. Then, a characteristic line indicating the relationship between the determined disconnection time H and the determined wiring temperature T is determined.

In this way, the activation energy Ea and the EM lifetime can be easily obtained from the obtained characteristic lines.

[0012]

FIG. 1 shows an example of an evaluation apparatus to which the present invention is applied. This evaluation device estimates the EM life and activation energy of aluminum wiring. A wafer 2 is mounted on a temperature control base (heating means) 1 and an insulating material (not shown) is placed on the wafer 2. Probe needles (measuring means) 4 and 4 are in contact with both ends of the aluminum wiring 3 of a predetermined pattern laid through the film.

The temperature control base 1 has a built-in heater (not shown) and a temperature sensor (not shown). The heater is energized from a DC power supply or a commercial AC power supply (not shown) through a controller 5. ing. The temperature sensor is disposed near the boundary surface with the wafer 2. The controller 5 is under PCM control by a microcomputer (wiring temperature calculation means, evaluation means) 6, and the temperature sensor outputs a detected temperature to the microcomputer 6.

On the other hand, the probe needles 4, 4 are supplied with a constant current from a constant current source (energizing means) 7, and the voltage across the probe needles 4, 4 is supplied to an amplifier (measuring means) 8, an A / D converter ( It is transmitted to the microcomputer 6 via the measuring means 9. FIG. 2 is an enlarged view of a main part in detail. The aluminum wiring 3 is heated by applying a constant current to the wafer 2, and the heat generated in the aluminum wiring 3 is radiated to the outside, particularly to the temperature control base 1.
Therefore, the temperature of the aluminum wiring 3 is controlled by adjusting the temperature of the temperature control base 1.

Hereinafter, the evaluation method of this embodiment will be described with reference to the flowcharts of FIGS. First, the temperature control base 1 is set to the set temperature Ta = 25 ° C. (100). This temperature control is performed by detecting a detected temperature and a set temperature Ta from a temperature sensor.
This is easily performed by feedback-controlling the on-duty ratio of the controller 5 according to the difference between
Since such control itself is well known, further description is omitted.

Next, after the detected temperature has reached the set temperature Ta, a command is sent to the constant current source 7 to supply a constant current Ic to the aluminum wiring 3.
(Current density J = 7.7 × 10 ⁶ A / cm ² ) is supplied (102), and at the same time, a built-in timer is started to count the accumulated energizing time (104). Next, after a lapse of time sufficient for the temperature distribution state due to the heat generation of the aluminum wiring 3 due to the energization to reach an equilibrium, the voltage V across the both ends of the aluminum wiring 3 is detected. Value R
Is calculated (V / Ic) and stored (106).

Thereafter, the voltage V at both ends of the aluminum wiring 3 is detected, and when the voltage V exceeds a predetermined voltage value Vth, it is determined that the aluminum wiring 3 is disconnected (108), and the count value of the built-in timer (108) That is, the disconnection time H) is stored, the timer is reset to 0, the counting is stopped (110), and the routine ends. Thus, a pair of the resistance value R and the disconnection time H is obtained.

Hereinafter, set temperatures Ta = 25 ° C., 50 ° C., 7
A large number of samples are prepared for each 5 ° C., and the resistance R and the disconnection time H are determined for each sample by the same process as described above.
Is measured. Next, a wiring temperature T is obtained for each of these resistance values R (201). In order to calculate the wiring temperature T from each resistance value R, the TCR (resistance temperature coefficient) of the aluminum wiring 3 must be determined in advance.
Is measured, and the wiring temperature T may be calculated from the TCR and each resistance value. The relational expression among the resistance value R, the wiring temperature T, and the resistance temperature coefficient TCR is shown below.

[0019] Next, the reciprocal of the obtained wiring temperature T is obtained (202), the logarithmic value of the disconnection time H is obtained (203), and the obtained value is Arrhenius plotted (204).
(See FIG. 3) (205).

Next, the activation energy Ea and the proportionality constant A are determined from the characteristic line L1 and the following theoretical formula (20).
6) End the routine. The activation energy Ea of the aluminum wiring 3 obtained in this experiment was 0.72 ev, which was in good agreement with the value 0.68 ev obtained by the conventional method. Here, the EM life H represents MTF (mean time to failure),
w is the wiring width, t is the wiring thickness, J is the current density, A is the proportional constant, K is the Boltzmann constant, Ea is the activation energy, T
Is the wiring temperature (absolute temperature).

FIG. 3 shows the characteristic line L1 obtained in this manner, and also shows the experimental value P in the conventional method at a current density J = 1 × 10 ⁶ A / cm ² . Next, the characteristic line L1
Above-mentioned method of (current density ^{J 7.7 × 10 6 A / cm} 2) to
The characteristic line L2 when the current density J is 1 × 10 ⁶ A / cm ² is obtained by the theoretical formula . Such current density ^{J = 1 × 10 6 A /} cm 2 at the characteristic line L2 obtained by the conventional way
It is in good agreement with the experimental value P obtained in the experiment by the method . What
FIG. 4 shows the current carrying density for each set temperature of the temperature control base.
The relationship between the temperature and the wiring temperature is shown.

As described above, according to this embodiment,
The activation energy Ea and the EM lifetime H can be calculated with high accuracy despite a simple configuration and operation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of an evaluation device of the present invention.

FIG. 2 is an enlarged sectional view of a main part of FIG.

FIG. 3 is a graph obtained by Arrhenius plot of measurement data.

FIG. 4 is a characteristic diagram showing a relationship among a current density, a base temperature, and a wiring temperature.

FIG. 5 is a flowchart showing one embodiment of the evaluation method of the present invention.

FIG. 6 is a flowchart showing one embodiment of the evaluation method of the present invention.

FIG. 7 is a conceptual diagram of the present invention.

[Explanation of symbols]

 FIG. 1 shows an example of an evaluation device to which the present invention is applied. 1 is a temperature control base (temperature maintaining means), 3 is aluminum wiring (wiring), 4 is a probe needle (measuring means), 6 is a microcomputer (wiring temperature calculating means, evaluating means), and 7 is a constant current source (energizing means). , 8 is an amplifier (measuring means), 9 is an A / D converter (measuring means).

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 31/02 G01R 27/08 H01L 21/66

Claims (2)

(57) [Claims] 1. A test apparatus, wherein wiring is laid on an insulator, is maintained at a plurality of predetermined temperature states, and is fixed to said wiring.
It energized a constant current at a current density, wherein each resistance value and each disconnection time of the wiring for each temperature condition was determined, on the basis of the resistance temperature coefficient of the measured resistance values and advance the wire
A method for evaluating a wiring, comprising calculating a temperature of each wiring, and determining a relationship between each disconnection time and a temperature of each wiring. 2. A temperature maintaining means for maintaining a test object in which wiring is laid on an insulator at a plurality of predetermined temperature states; an energizing means for applying a constant current to the wiring at a constant current density ; Measuring means for measuring each resistance value and each disconnection time of the wiring for each temperature state, and a wiring temperature for calculating the temperature of each wiring based on each resistance value and a previously measured resistance temperature coefficient of the wiring. Calculating means, based on a relationship between each of the wiring temperatures and each of the disconnection times,
Evaluation means for estimating a disconnection time or an activation energy of the wiring at an arbitrary wiring temperature.