JPH11163071A - Mos capacitor for damage evaluation and method for damage evaluation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform damage evaluation of a MOS capacitor insulating film with precision, by setting the circumferential length of the top-view of a capacitive insulating film to a specific multiple of the circumferential length of a square with the identical area to that of the capacitive insulating film. SOLUTION: On the surface of a silicon substrate 1 which is a lower part electrode, a field insulating film 2 is selectively formed. By this, an element region is partitioned and on the surface of a partitioned block region, an active oxide film (capacitive insulating film) 3 is formed with a film thickness thinner than the field oxide film 2 (for example, film thickness of 90 Å). The active oxide film 3 is formed with a rectangular top view, and its circumferential length is set to be about 2.5 times that of a square with the identical area as the area of the active oxide film. Further, on the active oxide film 3, an upper part electrode 4 of polysilicon of, for example, antenna ratio of 350000 is formed. Thus, a minute leakage current is measured, for accurate evaluation of minute damage degree.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the damage of an insulating film (silicon oxide film) generated during plasma processing when manufacturing a semiconductor device such as an LSI. The present invention relates to a damage-evaluating MOS capacitor and a damage-evaluating method that can be evaluated in a reliable manner.

[0002]

2. Description of the Related Art In recent years, in a plasma processing process such as an LSI etching process, a resist removing process, and an ion implantation process, an insulating film (silicon oxide film: SiO ₂ ) is broken or damaged by a charge-up phenomenon. Is a problem. The breakdown and damage of the insulating film due to the charge-up phenomenon (charge-up damage) is caused by the fact that static electricity is accumulated (charge-up) in the upper electrode of the semiconductor device during the plasma processing step, and the accumulated static electricity is accumulated in the gate region of the transistor This is caused by discharge through the formed thin insulating film (active oxide film). As a result, destruction or deterioration of the active oxide film occurs, and the yield of products is significantly reduced. Such charge-up damage is caused by non-uniform plasma potential or by processing a fine pattern on a film on a wafer.

Various methods have been proposed for evaluating the charge-up damage of an insulating film. Among these evaluation methods, one of the effective methods is a MOS (Metal-Oxide) with an antenna. -Semiconducto
r) Method of measuring current-voltage characteristics of capacitor (IV
(Hyungcheol Shin et al., “Modeling Oxid
e Thickness Dependence of Charging Damage by Plasm
a Processing '', IEEE ELECTRON DEVICE LETTERS, VOL.
14, NO.11, (1993), pp.509-511, Mizutani et al., "Radiation damage of SiO ₂ / Si by plasma processes", Applied Physics, Vol. 59, No. 11, (1990), pp.1496 -1501).
The IV measurement method is a method of measuring IV characteristics before and after plasma processing, and comparing these to evaluate charge-up damage.

FIG. 7 is a sectional view showing the structure of a MOS capacitor with an antenna. An oxide film 27 is formed on a silicon substrate 26. The oxide film 27 is selectively formed with a region (active oxide film 27a) thinner than other regions. On the active oxide film 27a and the oxide film 27, an upper electrode (antenna) 28 is formed in a region wider than the active oxide film 27a, thereby forming a MOS capacitor 29. Here, the ratio (Se / So) of the area Se of the upper electrode (antenna) to the area So of the active oxide film is called an antenna ratio. As described above, when the upper electrode 28 is formed in a region wider than the active oxide film 27a, the current flowing from the plasma is amplified by the upper electrode 28 and injected into the active oxide film 27a in the plasma processing step. . Therefore, the detection sensitivity of the charge-up damage by the MOS capacitor with the antenna is proportional to the antenna ratio.

[0005] As a method of measuring the IV characteristics, generally,
By gradually increasing the voltage applied to the MOS capacitor,
A method of measuring a current value flowing from an electrode to a substrate has been used. FIG. 8 is a graph showing an example of general IV characteristics, with current being plotted on the vertical axis and voltage on the horizontal axis. FIG.
As shown in (1), when the voltage applied to the upper electrode 28 of the MOS capacitor 29 is increased, a leak current 30a is generated. The leak current 30a slightly increases as the voltage value increases until it reaches a certain voltage value. When the voltage applied to the upper electrode 28 exceeds about 6 (MV / cm), the FN tunnel current 30b starts flowing. The FN tunnel current is a phenomenon in which, when a large voltage (electric field) is applied to an insulating film (oxide films 27 and 27a), electrons move to a conduction band of the insulating film due to a tunnel phenomenon, and a current flows. is there.

Thereafter, when the voltage applied to the upper electrode 28 of the MOS capacitor 29 is further increased, about 12 (MV
/ Cm) irreversible dielectric breakdown by applying a voltage of 30c
Occurs. As an evaluation method for evaluating the damage of the insulating film from such IV characteristics, a voltage region (about 6 to 12 (MV / cm)) where the FN tunnel current flows is used.
The most commonly used method is to measure a voltage value (GOI voltage) when a predetermined current value (for example, 5 (mA / cm ² )) is reached.

However, the IV characteristic in the FN tunnel region hardly changes at the beginning of plasma damage, but changes abruptly at the final stage of damage, leading to dielectric breakdown. In this case, the measured GOI voltage is a healthy value or a value near zero (dielectric breakdown state), and does not show an intermediate value. Therefore, in the IV measurement method, the magnitude of the damage of the insulating film is determined only in two stages of Good and No-Good, and it is difficult to evaluate the intermediate magnitude of the damage and the continuous magnitude relation of the damage. It is.

Therefore, the present inventors have found that when the voltage applied to the electrode is in the range of 0.3 to 6 (MV / cm), the leakage current generated through the active oxide film is
They found that the amount of charge-up damage was closely related, and reported this (Y. Fukumoto et al., "Beh
aviors of Plasma-Induced Pre-Tunneling Leakage Cur
rent in MOS Capacitor '', 2nd International Symposi
um on Plasma Process-Induced Damage, (1997), pp.99
-101). Utilizing this, the voltage is, for example, 4 (MV / c
By measuring the leak current at the time of m), the magnitude of the charge-up damage can be evaluated.

[0009] The leakage current is caused by minute damage to such an extent that the GOI voltage does not change, and the magnitude of the leakage current changes continuously depending on the magnitude of the damage. Therefore, according to the method of evaluating the magnitude of damage by measuring the leakage current, compared with the method of evaluating the magnitude of damage by measuring the GOI voltage, when a MOS capacitor having the same antenna ratio is used, Charge-up damage can be measured with high sensitivity. Also,
According to this evaluation method, it is possible to evaluate the intermediate damage and the continuous magnitude relationship between the damages.

[0010]

As described above, the magnitude of the charge-up damage is closely related to the magnitude of the leak current.
In order to evaluate even smaller damage using a capacitor, it is necessary to detect a smaller leak current. The lower limit of the current value that can be measured is
The lower limit of the current value recognized as the leak current is generally about 100 fA, which is determined by the measuring device and environment to be used. Therefore, in order to detect minute damage that causes a leak current smaller than this limit value, the leak current is increased by increasing the area of the active oxide film, or the damage detection sensitivity is increased by increasing the antenna ratio. Need to be increased. However, if an attempt is made to increase the area of the active oxide film or the antenna ratio in order to detect minute damage, the area occupied by the upper electrode (antenna) on the wafer becomes large, thereby increasing the area of the device. The problem occurs.

The present invention has been made in view of such a problem, and it is possible to measure a small leak current without increasing the area of a device, thereby accurately determining the degree of minute damage. It is an object to provide a damage evaluation MOS capacitor and a damage evaluation method that can be evaluated.

[0012]

A MOS capacitor for damage evaluation according to the present invention comprises a semiconductor substrate, a capacitor insulating film formed on the semiconductor substrate, and an electrode formed on the capacitor insulating film. Wherein the perimeter of the capacitance insulating film in plan view is 1.2 to 20 times the perimeter of a square having the same area as the area of the capacitance insulating film. MOS capacitor for damage evaluation.

According to the damage evaluation method of the present invention, a semiconductor substrate and a capacitor insulating film formed on the semiconductor substrate and having a peripheral length of 1.2 to 20 times the peripheral length of a square having the same area as the semiconductor substrate are provided. After subjecting the damage evaluation MOS capacitor having the electrode formed on the capacitive insulating film to plasma treatment, the dielectric breakdown voltage of the MOS capacitor is set at 5%.
A leakage current generated by applying a voltage of about 70% to the MOS capacitor is measured, and a degree of charge-up damage of the semiconductor device when the semiconductor device is subjected to plasma processing is evaluated based on a leakage current of the damage evaluation MOS capacitor. It is characterized by the following.

In the present invention, the capacitance insulating film is
A thin insulating film surrounded by a field insulating film, which is an insulating film in a region functioning as a capacitor.

In the present invention, the peripheral length of the capacitance insulating film of the MOS capacitor for damage evaluation is 1.2 to 20 times the peripheral length of a square having the same area as the area of the capacitance insulating film. Using such a MOS capacitor,
When evaluating the damage of a semiconductor device, first, the MO
A predetermined plasma process is performed on the S capacitor. After that, 5 to 70% of the breakdown voltage of the MOS capacitor
Is applied to the electrode of the MOS capacitor, and the generated leakage current is measured. When the capacitance insulating film of the MOS capacitor is damaged and the magnitude of the damage is constant, the measured leak current increases in proportion to the peripheral length of the capacitance insulating film.

In the present invention, since the peripheral length of the capacitive insulating film is appropriately defined as described above, it is difficult to measure with a normal measuring device when the capacitive insulating film is slightly damaged. Even if a small leak current occurs, the leak current is amplified. Therefore, the generated leakage current can be accurately measured, and the degree of damage to the capacitance insulating film of the MOS capacitor can be evaluated with high accuracy. Then, the degree of charge-up damage of the semiconductor device when the semiconductor device is subjected to plasma processing can be evaluated based on the value of the leak current.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a MOS capacitor for damage evaluation according to the present invention will be described with reference to the accompanying drawings. FIG. 1A is a sectional view showing a structure of a damage evaluation MOS capacitor according to a first embodiment of the present invention, and FIG. 1B is a plan view showing an example of a shape of an active oxide film.

As shown in FIG. 1A, a field insulating film 2 is selectively formed on the surface of a silicon substrate 1 serving as a lower electrode, thereby defining an element region. An active oxide film (capacitive insulating film) 3 having a smaller thickness (for example, a thickness of 90 °) than the field insulating film 2 is formed on the surface of the partitioned element region. As shown in FIG. 1B, the active oxide film 3 is formed in a rectangular shape in a plan view, and its peripheral length is about 2.10 times the peripheral length of a square having the same area as the active oxide film 3. 5 times. Further, on the active oxide film 3,
For example, an upper electrode 4 made of polysilicon having an antenna ratio of 350,000 is formed. Thus, a damage evaluation MOS capacitor is formed.

The MO for damage evaluation constructed as described above
When evaluating damage to a semiconductor device using an S capacitor, first, for this MOS capacitor,
Plasma treatment is performed under predetermined conditions. Since the active oxide film 3 is slightly damaged by the plasma processing, when a predetermined voltage is applied to the upper electrode 4, a small leak current is generated in proportion to the magnitude of the damage. Conventionally, when measuring a leak current less than the lower limit of the current that can be measured by the measuring device, the area of the upper electrode is increased to increase the antenna ratio, or the area of the active oxide film is increased. As a result, it is necessary to amplify the leak current until the leak current becomes equal to or higher than the detection limit, thereby improving the damage detection sensitivity.

In this embodiment, the active oxide film 3
Is about 2.5 times as large as a square-shaped peripheral length having the same area as that of the active oxide film 3, and a MOS having a square-shaped active oxide film having the same area as the active oxide film 3 is formed. It is possible to obtain about 2.5 times the leakage current as compared with the capacitor. Therefore, by measuring the leak current amplified until it exceeds the detection limit and calculating the leak current that actually occurs based on the value,
The degree of damage to the active oxide film of the MOS capacitor can be evaluated, whereby the degree of damage to the semiconductor device caused by the plasma processing can be accurately evaluated.

Here, regarding the relationship between the magnitude of the leakage current of the MOS capacitor and the perimeter of the active oxide film,
This will be described in detail. FIG. 2A is a plan view showing a wafer on which chips are formed, and FIG. 2B is an enlarged plan view showing the chips. FIG. 3 is a plan view showing active oxide films of various shapes.

First, a plurality of chips 6 were formed on the entire surface of an 8-inch wafer 7 and used as an evaluation wafer. On each chip 6, three types of MOS capacitors (capacitor A, capacitor B and capacitor C) having a structure similar to the structure shown in FIG. 1A are formed. However, FIG.
As shown in (a), the length of one side of the capacitor A is 10
It has a square active oxide film 3a having a size of μm, and as shown in FIG.
It has a rectangular active oxide film 3b of μm × 50 μm. As shown in FIG. 3 (c), the capacitor C has an active oxide film 3c having a shape in which two U-shaped parallel portions extend, and has a longitudinal length of 50 μm. The width of one parallel portion is 1 μm, and the interval between the parallel portions is 1 μm. Therefore, the area of each of these active oxide films 3a, 3b and 3c is about 100 μm.
m ² , the peripheral length of the active oxide film 3b is about 2.5 times the peripheral length of the active oxide film 3a, and the peripheral length of the active oxide film 3c is about 5 times the peripheral length of the active oxide film 3a. is there. As shown in FIG. 2B, the upper electrodes 4a, 4b and 4c of the capacitors A, B and C
Are processed into an antenna shape separated by wet etching, these areas are all the same, and the antenna ratio is about 350,000.

Next, the wafer 7 is set in a plasma ashing apparatus, and the wafer 7 is subjected to plasma ashing as a LSI manufacturing process under predetermined conditions (gas type, gas pressure, high frequency plasma power and bias voltage). Processing was performed. Next, the processed wafer was placed in a prober evaluation apparatus, and the IV (current-voltage) characteristics of each device were measured. FIG. 4 is a graph showing the relationship between the magnitude of the leak current and the perimeter of the active oxide film, with the vertical axis representing the leak current and the horizontal axis representing the perimeter ratio of the active oxide film. However, the perimeter ratio is a ratio to the perimeter of the capacitor A, and the leakage current is a value when a voltage of 4 V, which is about 50% of the breakdown voltage of the MOS capacitor, is applied.

It is known that when plasma processing conditions are constant, the magnitude of charge-up damage to the active oxide film of each device is proportional to the antenna ratio. Since the capacitors A, B, and C have the same antenna ratio, the magnitude of the damage given to these capacitors is the same. On the other hand, as shown in FIG. 4, when the leak current of capacitors A, B and C is measured at the same voltage, this leak current increases in proportion to the perimeter of the active oxide film. This indicates that when measuring devices having the same voltage sensitivity are used, if the peripheral length of the active oxide film is set to N times, the maximum sensitivity for detecting damage is improved by N times. In other words, by making the peripheral length of the active oxide film N times, it is possible to obtain the same result as in the case of measuring the leak current of the capacitor having the antenna ratio N times.

Therefore, when the leakage current under a predetermined voltage is measured using the MOS capacitor for damage evaluation according to the first embodiment shown in FIG. 1, a square shape having the same area as the active oxide film shown in FIG. 1 is obtained. In comparison with the case where a MOS capacitor having an active oxide film is used, a leak current about 2.5 times is observed. Therefore, without increasing the area of the active oxide film or the antenna ratio,
A minute leak current can be amplified and accurately measured, and the degree of minute damage to the semiconductor device can be evaluated.

In the first embodiment shown in FIG. 1, the perimeter of the active oxide film 3 is 2.5 times the perimeter of a square having the same area. However, the present invention is not limited to this. Not done. If the perimeter of the active oxide film is less than 1.2 times the perimeter of a square having the same area, the detection sensitivity of the leak current is also less than 1.2 times, and the degree of damage can be evaluated with high accuracy. Can not. On the other hand, when the perimeter of the active oxide film exceeds 20 times the perimeter of a square having the same area, the effect of improving the leak current detection sensitivity with respect to the increase in the perimeter of the active oxide film is saturated. Therefore, in the present invention, the peripheral length of the active oxide film is set to 1.2 to 20 times the peripheral length of the square having the same area.

Further, the shape of the active oxide film in plan view is not particularly limited, as long as it has a perimeter defined in the present invention, as shown in FIGS. 3 (b) and 3 (c).
And the like.

Furthermore, in the present invention, if the voltage for measuring the leak current is less than 5% of the breakdown voltage of the MOS capacitor, it becomes difficult to evaluate the degree of damage to the insulating film with high accuracy. . On the other hand, when the voltage for measuring the leak current exceeds 70% of the breakdown voltage of the MOS capacitor, the FN tunnel current starts to be generated. This FN
The IV characteristic of a MOS capacitor in a voltage region where a tunnel current occurs is not proportional to the perimeter of the active oxide film, but is proportional to the area of the active oxide film. Therefore, even if the GOI voltage is measured using the damage evaluation MOS capacitor according to the present embodiment, the degree of damage to the insulating film cannot be evaluated with high accuracy. Therefore,
In the present invention, the leak current is measured at a voltage of 5 to 70% of the breakdown voltage of the MOS capacitor.

Furthermore, in this embodiment, the MOS capacitor was subjected to plasma processing by a plasma ashing apparatus to measure the charge-up damage caused by the plasma ashing. However, in the damage evaluation method according to the present invention, the MOS capacitor was etched. When the leak current is measured after performing plasma treatment with the apparatus and the ion implantation apparatus, charge-up damage of the semiconductor device due to etching or ion implantation can be measured.

As described above, when the plasma processing conditions are constant, the degree of damage to the insulating film does not depend on the structure of the device. Therefore, as shown in the first embodiment, a simple three-layer structure is used. The degree of damage to the insulating film can be evaluated using the MOS capacitor for damage evaluation.
However, the structure of the evaluation device is not limited to the structure shown in FIG. 1, and in the present invention, evaluation devices having various MOS capacitor structures can be used.

FIG. 5 is a sectional view showing the structure of a damage evaluation MOS capacitor according to a second embodiment of the present invention.
FIG. 6 shows an MO for damage evaluation according to the third embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a structure of an S capacitor. In the MOS capacitors shown in FIGS. 5 and 6, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The MOS capacitor for damage evaluation shown in FIG. 5 is obtained by selectively forming a photoresist film 9 on a polysilicon film 8 before processing the upper electrode 4 shown in FIG. Also, the MOS for damage evaluation shown in FIG.
The capacitor has an interlayer insulating film 10 formed on the entire surface including the upper electrode 4 and the field insulating film 2, and the interlayer insulating film 10 has a contact hole 10 a in a region matching the active oxide film 3. Further, a metal film 11 is formed on the interlayer insulating film 10 and inside the contact hole 10a.

The MO for damage evaluation constructed as described above
Also with the S capacitor, the peripheral length of the active oxide film is set to 1.2 to 20 times the peripheral length of the square having the same area as the active oxide film, similarly to the first damage evaluation MOS capacitor shown in FIG. As a result, the leakage current is amplified to 1.2 to 20 times. Therefore, the degree of damage to the active oxide film of the MOS capacitor can be evaluated by measuring the amplified leak current and calculating the actually generated leak current based on the value. As a result, the degree of minute damage to the semiconductor device caused by the plasma processing can be accurately evaluated.

[0034]

As described in detail above, according to the present invention,
The perimeter of the capacitance insulating film of the MOS capacitor is appropriately defined, and if the capacitance insulating film is damaged by the plasma processing, the measured leakage current increases in proportion to the perimeter of the capacitance insulating film. Leakage current below the detection limit can be accurately measured. Further, according to the method of the present invention, when a predetermined voltage is applied to the electrodes after performing a predetermined plasma treatment on the MOS capacitor, the generated leakage current can be amplified and measured accurately. The degree of damage to the insulating film of the capacitor can be evaluated with high accuracy, and by using this,
The degree of charge-up damage of the semiconductor device when the semiconductor device is subjected to plasma processing can be evaluated.

[Brief description of the drawings]

FIG. 1A is a sectional view showing a structure of a damage evaluation MOS capacitor according to a first embodiment of the present invention;
(B) is a plan view showing an example of the shape of the active oxide film.

2A is a plan view showing a wafer on which chips are formed, and FIG. 2B is an enlarged plan view showing the chips.

FIG. 3 is a plan view showing active oxide films of various shapes.

FIG. 4 is a graph showing the relationship between the magnitude of the leak current and the perimeter of the active oxide film, with the vertical axis representing the leak current and the horizontal axis representing the perimeter ratio of the active oxide film.

FIG. 5 shows a damage evaluation M according to a second embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a structure of an OS capacitor.

FIG. 6 shows a damage evaluation M according to a third embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a structure of an OS capacitor.

FIG. 7 is a sectional view showing a structure of a MOS capacitor with an antenna.

FIG. 8 is a graph showing an example of general IV characteristics, with current being plotted on the vertical axis and voltage on the horizontal axis.

[Explanation of symbols]

 1, 26; Substrate 2: Field insulating film 3, 3a, 3b, 3c, 27a; Active oxide film 4, 4a, 4b, 4c, 28; Upper electrode 6; Chip 7; Wafer 8; Polysilicon film 9; Film 10; interlayer insulating film 11; metal film 27; oxide film 29; MOS capacitor 30a; leak current 30b; FN tunnel current 30c;

Claims (2)

[Claims] 1. A damage evaluation MOS capacitor comprising: a semiconductor substrate; a capacitance insulating film formed on the semiconductor substrate; and an electrode formed on the capacitance insulating film. Wherein the perimeter in plan view is 1.2 to 20 times the perimeter of a square having the same area as the area of the capacitive insulating film. 2. A semiconductor substrate, a capacitor insulating film formed on the semiconductor substrate and having a peripheral length of 1.2 to 20 times the peripheral length of a square having the same area as the semiconductor substrate; For evaluating damage having electrodes formed on the substrate
After subjecting the capacitor to plasma treatment, a leakage current generated by applying a voltage of 5 to 70% of the breakdown voltage of the MOS capacitor to the MOS capacitor is measured, and charge-up of the semiconductor device when the semiconductor device is subjected to plasma treatment. A damage evaluation method, wherein a degree of damage is evaluated by a leak current of the damage evaluation MOS capacitor.