JPH11145236A - Plasma-damage evaluating method and apparatus thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the uniformity of a plasma, by exposing to the plasma a first conductor connected with a gate electrode and a second conductor connected with a diffusion layer of the opposite conductivity type to the first conductor, and by inspecting thereafter the plasma damage of a gate insulation film. SOLUTION: A gate pad 10 and well pad 11 exposed to a plasma are charged respectively in response to the plasma states of their existing places. In this case, when the plasma states of the positions of the respective pads 10, 11 are equal to each other, the potentials of a gate electrode 5 and N-well 2 are also made equal to each other. That is, no electric field is applied to a gate insulation film 4 not to damage it. However, when the plasma states of the positions of the gate pad 10 and well pad 11 are different from each other, the respective pads 10, 11 are charged to different potentials to make the potentials of the gate electrode 5 and N-well 2 also different from each other. This potential difference is applied to the gate insulation film 4 to damage it. When measuring the damage of the gate insulation film 4, the plasma state separated therefrom by the distance between the pads 10, 11 can be known.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for evaluating a gate insulating film, and more particularly to a method for evaluating plasma damage of a gate insulating film caused by a semiconductor manufacturing process.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, there are many processes using plasma. During these plasma processes, the wafer is electrically charged, causing damage to the gate insulating film, causing problems such as lowering the yield of LSI and deteriorating reliability. Conventionally, a semiconductor element having an antenna structure is used in order to detect a gate insulating film damage caused by such a cause with high sensitivity. For example, Japanese Patent Publication No. 7-7751, USP-5,
548,224 describe such an example. However, the former relates to a method of detecting a charge-up in a MOS manufacturing process, not to a damage of a gate oxide film in a plasma process, and the latter U.S. Pat. A method for predicting the reliability of an oxide thin film by leakage current or charge induction is disclosed.

Here, an example in which the gate electrode becomes an antenna will be described below with reference to FIGS. 10 and 11. Note that an X-Y cross section in FIG. 11 corresponds to FIG.

As shown in the sectional view of FIG. 10, a gate insulating film 104 is provided on a semiconductor substrate 101 in a region surrounded by a field oxide film 103 for element isolation such as LOCOS. Next, a gate electrode 5 covering the gate insulating film 104 and extending to the field oxide film 103 is provided. In such a configuration, when the gate electrode 105 is exposed to a plasma process, electric charges from the plasma are transferred to the gate electrode 1.
05. When the amount of charge on the gate electrode 105 is large, the potential of the gate electrode 105 becomes higher than the potential of the semiconductor substrate 101. If this potential difference is sufficiently large, the gate insulating film 104 causes dielectric breakdown,
Current flows to the semiconductor substrate 1. As shown in the plan view of FIG. 11, assuming that the gate electrode area of the gate electrode 105 on the gate insulating film 104 is Ag and the total area of the gate electrode is Af, the larger the area ratio Af / Ag of the area Af and Ag, the larger the gate. The amount of current flowing through the insulating film 104 is large, so that the gate insulating film 104 is also greatly damaged.

The measurement for determining the plasma damage amount of the gate insulating film 104 includes the leak current, the withstand voltage, the charge amount that can be injected before the gate insulating film 104 is broken, the interface state density, and the flat band voltage. Used as an indicator.

[0006] Since the semiconductor substrate 101 is a single conductor, the potential of the semiconductor substrate 101 during the plasma process is constant irrespective of the location of the wafer. On the other hand, the gate electrode 105
Can vary with the state of the plasma at that location. Therefore, when the state of the plasma is non-uniform at various locations on the wafer, the potential of the gate electrode 105 is also non-uniform on the wafer. That is, the potential difference between the gate electrode 105 and the semiconductor substrate 101 differs depending on the position on the wafer, and the degree of damage to the gate insulating film 104 also differs depending on the position on the wafer. Therefore, by examining the dependence of the damage of the gate insulating film 104 on the position in the wafer surface, it is possible to obtain information on the non-uniformity of the plasma. If the degree of plasma non-uniformity can be known, the plasma process can be improved, which leads to an improvement in the semiconductor manufacturing process.

[0007]

However, the above-mentioned prior art has the following problems.

To know whether the plasma is uniform,
It was necessary to measure semiconductor devices at a plurality of locations in the wafer plane. Furthermore, quantitative information about the uniformity of the plasma can be obtained only by comparing the data at each measurement location with each other. For this reason, there is a problem that the number of measurement points is increased and it takes time to analyze data.

[0009] Further, since plasma damage occurs with reference to the potential of the semiconductor substrate, for example, if the contact between the semiconductor substrate and the wafer chuck is not sufficient, the potential of the semiconductor substrate will not be stable, and the measurement result of the gate insulating film damage will be as follows. There is also a problem that the non-uniformity of the plasma is not correctly reflected.

[0010] The object of the present invention is to provide a method for evaluating a semiconductor device, in which the degree of plasma uniformity in a wafer surface can be known from a simple measurement. In particular, it is an object of the present invention to provide an evaluation method capable of quantitatively knowing the degree of uniformity of plasma from a short distance to a long distance and improving accuracy, reliability, and operability thereof.

[0011]

According to the present invention, there is provided a method and an apparatus for evaluating plasma damage, comprising: a well of opposite conductivity type provided on a semiconductor substrate of one conductivity type; and a predetermined space on the well of opposite conductivity type. A field insulating film provided on the surface of the one-conductivity-type semiconductor substrate having a first opening and a second opening separated by a distance, and the opposite-conductivity-type well in the first opening A gate insulating film provided on the surface of the gate insulating film, a gate electrode provided on the field insulating film so as to cover at least a part of the gate insulating film, and the reverse conductivity type well in the second opening. A first conductor connected to the gate electrode, and a second conductor connected to the opposite conductivity type diffusion layer, the semiconductor device having: Conductor and said second conductor to a plasma process After the Rashi, it is characterized by examining the plasma damage to the gate insulating film.

As another mode, a first reverse conductivity type well provided on a semiconductor substrate of one conductivity type, and a first one conductivity type well provided on a surface portion in the first reverse conductivity type well are provided. A field insulation provided in the one conductivity type semiconductor substrate, the first conductivity type well having a first opening and a second opening at a predetermined distance apart from each other on the first one conductivity type well; A film, a gate insulating film provided on the surface of the first one-conductivity-type well in the first opening, and provided to extend over the field insulating film so as to cover at least a part of the gate insulating film. Gate electrode and a first gate electrode in the second opening.
Using a semiconductor device having a diffusion layer provided in one well of one conductivity type, a first conductor connected to the gate electrode, and a second conductor connected to the diffusion layer of the opposite conductivity type. After exposing the first conductor and the second conductor to a plasma process, the gate insulating film is inspected for plasma damage.

[0013] The present invention is characterized in that a plurality of the semiconductor devices having different values of the predetermined interval are evaluated to evaluate plasma non-uniformity.

[Operation] In the semiconductor device of the present invention, the voltage applied to the gate insulating film due to charging during the plasma process is determined by the potential of the gate pad and the potential of the well pad. By providing the pads separated by a predetermined distance, the uniformity of the plasma at a location separated by the distance between the pads can be checked. In addition, a plurality of semiconductor elements having different inter-pad distances are used to quantitatively examine the uniformity depending on the location of plasma.

[0015]

Next, a method for evaluating plasma damage according to the present invention will be described in detail with reference to the drawings. In the present embodiment, a case where charging by plasma occurs in a wiring process, that is, a case where the wiring serves as an antenna will be described. The plasma process includes a plasma etching step for forming a wiring, a plasma etching step, a step of forming an insulating film by plasma CVD, and the like.

[First Embodiment] FIG. 1 is a sectional view showing a first embodiment of a semiconductor device used for evaluating plasma damage according to the present invention. FIG. 2 is a plan view of a semiconductor device corresponding to FIG. The XY section in FIG. 2 corresponds to FIG.

As shown in FIG. 1, an N-well 2 having a constant depth is provided on the surface of a P-type semiconductor substrate 1. On the P-type semiconductor substrate 1, a field oxide film 3 such as LOCOS having openings at two positions separated from each other in an N well 2 is formed.
Is provided. A gate insulating film 4 is provided on the surface of the N well 2 on the P-type semiconductor substrate 1 in one opening. A gate electrode 5 is provided to cover a part of field oxide film 3 and gate insulating film 4. An N-type diffusion layer 6 is provided in the N well 2 in the other opening.

An interlayer insulating film 7 is provided to cover the entire area including the field oxide film 3, the gate electrode, and the N-type diffusion layer. In the interlayer insulating film 7, a contact 8 reaching the gate electrode 5 and a contact 9 reaching the N-type diffusion layer 6 are provided. A pad is provided on the contact 8 and becomes a gate pad 10 connected to the gate electrode 5. A pad is provided on the contact 9 and becomes a well pad 11 connected to the N-type diffusion layer 6 on the N well 2. The gate pad 10 and the well pad 11 are separated from each other, and the distance between the pads at the center of the pad is D. It is assumed that the inter-pad distance D is larger than the pad size.

When such a semiconductor device is exposed to a plasma process, it is charged as follows. The pads 10, 11 exposed to the plasma are charged according to the state of the plasma at that location. That is, the gate electrode 5 is charged by the plasma at the position of the gate pad 10 and has a certain potential. On the other hand, the well pad 11 is also charged by the plasma at that position, and the potential of the N well 2 connected to the well pad 11 becomes a certain potential.

At this time, if the plasma at the position of the gate pad 10 and the position of the well pad 11 are in the same state, the gate pad 10 and the well pad 11 are charged to the same potential, and the gate electrode 4 and the N well 2 are charged. Becomes the same. That is, no electric field is applied to the gate insulating film 4, and no damage occurs. However, if the plasma at the position of the gate pad 10 is different from the plasma at the position of the well pad 11, the gate pad 10 and the well pad 11 are charged to different potentials, and the gate electrode 4 and the N well 2 are charged.
Are also different. This potential difference is applied to the gate insulating film 4, and the possibility of causing damage increases.

Therefore, by measuring the damage of the gate insulating film 4 of such a semiconductor device, it is possible to know whether or not the plasma state is non-uniform at a place separated by the inter-pad distance D and to what extent. Can be. An element in which the distance D between the pads is variously changed is formed, and the gate insulating film 4 is formed.
By examining the dependence of the damage on the distance D between the pads, detailed information on the non-uniformity of the plasma can be obtained.

FIG. 9 shows an example of the measurement result. This is a plot of the yield rate of the gate insulating film 4 as a function of the inter-pad distance D of the semiconductor device of the present embodiment. When the distance D between the pads is 600 microns or less, no defect occurs. However, at 800 microns or more, the non-defective rate gradually decreases. That is, the distance on the wafer is 8
A distance of more than 00 microns indicates that the non-uniformity of the plasma is large enough to affect the yield rate of the gate insulating film 4. Therefore, it is considered that when the distance D between the pads is 800 microns or more, the state of the plasma becomes non-uniform.

The P-type semiconductor substrate 1 also has a certain potential. The polarity of the charging of the pads 10 and 11 by the plasma is often positive with respect to the potential of the semiconductor substrate 1. For this reason, the junction formed by the P-type semiconductor substrate 1 and the N-well 2 is biased in a reverse manner, so that the potential of the N-well 2 is held almost without being affected by the potential of the P-type semiconductor substrate 1. . That is, the semiconductor element having the structure in which the N well 2 is provided on the P-type semiconductor substrate 1 as in the present embodiment is effective when the polarity of the charging by the plasma is positive.

In the above embodiment, the MOS type transistor is not formed, especially since the diffusion layer 14 is located at one place. However, even when the source electrode and the drain electrode are arranged with the gate electrode interposed therebetween, the basic structure is not changed. Is similar, so
The configuration of the present embodiment includes transistors, diodes, resistors,
Similarly, when used for a capacitor or the like, it can be used for evaluating plasma damage.

[Second Embodiment] Next, a second embodiment of the semiconductor device used in the present invention will be described. FIG. 3 is a cross-sectional view showing a third embodiment of a semiconductor device used for evaluating plasma damage according to the present invention. FIG. 4 is an element plan view corresponding to FIG. The XY cross section in FIG. 4 corresponds to FIG.
3, reference numeral 12 denotes an N-type semiconductor substrate, 13 denotes a P-well formed in the N-type semiconductor substrate 12 by an ion implantation method or the like, and 14 denotes a diffusion layer formed in one opening of the field oxide film 3. In the other parts, the same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

The first embodiment is effective when the polarity of the charging of the pads 10 and 11 by the plasma is positive. When the polarity of the charging by the plasma is negative, the P-type semiconductor substrate 1 of the first embodiment is replaced with the N-type semiconductor substrate 12,
N well 2 is to P well 13 and N type diffusion layer 6 is
It only needs to be replaced with the mold diffusion layer 14. If the potential of the P well 13 is negative with respect to the potential of the N-type semiconductor substrate 12,
Since the junction formed by the P-well and the N-type semiconductor substrate is reversely biased, the potential of the P-well is not affected by the potential of the N-type semiconductor substrate.

[Third Embodiment] Next, a method of using a P-type semiconductor substrate even if the polarity of charging by plasma is negative will be described below as a third embodiment. FIG. 5 is a sectional view showing a third embodiment of a semiconductor device used for evaluating plasma damage according to the present invention. FIG. 6 is an element plan view corresponding to FIG. The XY cross section in FIG. 6 corresponds to FIG.

In the present embodiment, in the P-type semiconductor substrate 1,
A first N well 15 is provided, and a first P well 16 is further provided in the first N well 15. By doing this,
First P well 16 is separated from P type semiconductor substrate 1 via first N well 15. Further, the first N well 15
In order to make the potential of the P-type semiconductor substrate 1 the same as that of the P-type semiconductor substrate 1, the N-type diffusion layer 17 provided in the first N-well 15 and the P-type diffusion layer 18 provided in the P-type semiconductor 1
0 and are connected by the first wiring 21.

The same reference numerals are given to the same parts as those in FIG.
The areas of the take-out contacts 8, 9 of 0, 11 are also shown.

Further, the N well 2 described in the first embodiment
The semiconductor element formed in the second embodiment and the P element described in the second embodiment.
If the semiconductor element formed in the well 13 is formed on the same P-type semiconductor substrate, positive, negative, and bipolar charges can be checked.
This has the advantage that data on plasma non-uniformity can be obtained.

Here, when the well pad 11 is charged to the positive electrode by plasma, the P-type diffusion layer 14 and the first P well are charged to the same potential, and the first N well 15 also becomes forward. It is charged to the same potential. However, the first N well 15 and the P-type semiconductor substrate 1 are separated because they are in opposite directions. Therefore, by examining the dependency of the gate insulating film 4 on the distance D between the pads using the gate electrode 5, it is possible to easily examine the non-uniformity of the plasma.

On the other hand, when the well pad 11 is negatively charged by plasma, the P-type diffusion layer 14 and the first P
Since the wells are charged to the same potential and the first N well 15 is in the opposite direction, the first P well and the first N well 15 are separated. Therefore, by examining the dependency of the gate insulating film 4 on the distance D between the pads using the gate electrode 5, it is possible to easily examine the non-uniformity of the plasma.

[Fourth Embodiment] Next, a fourth embodiment of the semiconductor device used in the present invention will be described. FIG. 7 is a sectional view showing a fourth embodiment of a semiconductor device used for evaluating plasma damage according to the present invention. FIG. 8 is an element plan view corresponding to FIG. The XY section in FIG. 8 corresponds to FIG.

In this embodiment, the comb is formed so that the perimeter of the gate pad 10 and the well pad 11 is large in the first embodiment. In the step of plasma etching of the wiring, electric charges from the plasma enter the wiring through the side surface of the wiring, so that the antenna ratio can be increased by increasing the peripheral length. By doing so, the difference in the plasma state at each pad position is amplified and a large potential difference is applied to the gate insulating film. That is, by using the semiconductor element of the present embodiment, even if the difference in the plasma state is extremely small, it is possible to detect the difference.

[0035]

According to the present invention, the degree of plasma non-uniformity of a semiconductor device used in the present invention at a place separated by a predetermined distance can be determined by measuring one semiconductor device.
An effect that the number of times of measurement of the semiconductor element for examining the uniformity of the plasma may be smaller is required.

Further, by measuring a plurality of semiconductor elements in which the distance between the gate pad and the well pad is changed, it is possible to know the degree of local plasma fluctuation in the semiconductor chip. , More detailed data can be obtained.

Further, by comparing the measurement results of the semiconductor elements between different chips, it is possible to know the local plasma fluctuation over the entire surface of the wafer. This is important data for improving the plasma process.

Further, in the semiconductor device used in the present invention,
Since damage to the gate insulating film is determined only by the state of the plasma on the wafer, more accurate data on plasma non-uniformity can be obtained. In a conventional semiconductor device, the gate insulating film damage may not be stable due to the uncertainty of the potential of the semiconductor substrate due to fluctuations such as contact resistance between a plasma device and a wafer. There was a risk that the uniformity was not correctly reflected, but since such a problem was solved, an effect of obtaining accurate data on non-uniformity of plasma can be obtained.

Although the present invention has been described with reference to an example in which the pad is formed in a comb-like shape having an antenna effect so that the wiring becomes an antenna, the present invention is not limited to this. In some cases, the via on the wiring exposed to the plasma may serve as an antenna.

[Brief description of the drawings]

FIG. 1 is an element cross-sectional view showing a first embodiment of a semiconductor element used for evaluating plasma damage according to the present invention.

FIG. 2 is an element plan view showing a first embodiment of a semiconductor element used in the present invention.

FIG. 3 is an element cross-sectional view showing a second embodiment of a semiconductor element used in the present invention.

FIG. 4 is an element plan view showing a second embodiment of a semiconductor element used in the present invention.

FIG. 5 is an element cross-sectional view showing a third embodiment of a semiconductor element used in the present invention.

FIG. 6 is an element plan view showing a third embodiment of a semiconductor element used in the present invention.

FIG. 7 is an element sectional view showing a fourth embodiment of a semiconductor element used in the present invention.

FIG. 8 is an element plan view showing a fourth embodiment of a semiconductor element used in the present invention.

FIG. 9 is a graph showing a measurement example using the semiconductor device of the present invention.

FIG. 10 is an element sectional view showing a conventional semiconductor device.

FIG. 11 is an element plan view showing a conventional semiconductor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 P-type semiconductor substrate 2 N well 3 Field oxide film 4 Gate insulating film 5 Gate electrode 6 N-type diffusion layer 7 Interlayer insulating film 8, 9 Contact 10 Gate pad 11 Well pad 12 N-type semiconductor substrate 13 P well 14 P-type diffusion Layer 15 First N-well 16 First P-well 17 N-type diffusion layer 18 P-type diffusion layer 19, 20 Contact 21 First wiring

Claims (9)

[Claims] 1. An opposite conductivity type well provided on a semiconductor substrate of one conductivity type, and a first opening and a second opening at positions separated by a predetermined distance on the opposite conductivity type well. A field insulating film provided on the surface of the one conductivity type semiconductor substrate, a gate insulating film provided on the surface of the opposite conductivity type well in the first opening, and at least one of the gate insulating film. A gate electrode provided to extend over the field insulating film so as to partially cover the gate electrode; a reverse conductivity type diffusion layer provided in the reverse conductivity type well in the second opening; After exposing the first conductor and the second conductor to a plasma process using a semiconductor device having a first conductor to be connected and a second conductor to be connected to the opposite conductivity type diffusion layer, Inspecting a gate insulating film Evaluation method for zuma damage. 2. The method for evaluating a plasma damage according to claim 1, wherein the gate insulating film is inspected based on a characteristic of a non-defective rate of the gate insulating film with respect to a distance between the first conductor and the second conductor. A method for evaluating plasma damage. 3. The plasma damage evaluation method according to claim 1, wherein said one conductivity type is a P-type conductor, and said reverse conductivity type diffusion layer is an N-type diffusion layer. Evaluation method. 4. The method according to claim 1, wherein the first conductor and the second conductor are comb-shaped pads and are exposed to the plasma process. A method for evaluating plasma damage, characterized in that the shape is such that an antenna effect can be obtained. 5. A first substrate provided on a semiconductor substrate of one conductivity type.
A well of a first conductivity type, a first well of a first conductivity type provided on a surface portion in the first well of a first conductivity type, and a predetermined distance above the well of the first conductivity type. 1st in position
A field insulating film having an opening and a second opening provided on the one conductivity type semiconductor substrate, and being provided on a surface of the first one conductivity type well in the first opening. A gate insulating film, a gate electrode covering at least a part of the gate insulating film and extending to the field insulating film, and provided in a first one-conductivity-type well in the second opening. And a first conductor connected to the gate electrode, and a second conductor connected to the opposite conductivity type diffusion layer.
A method for evaluating plasma damage, comprising inspecting the gate insulating film after exposing the first conductor and the second conductor to a plasma process using a semiconductor device having the following conductors. 6. The plasma damage evaluation method according to claim 1, wherein a plurality of semiconductor devices having different values of the predetermined interval are used. 7. A reverse conductivity type well provided in a semiconductor substrate of one conductivity type, and a first opening and a second opening at positions separated by a predetermined distance on the reverse conductivity type well. A field insulating film provided on the surface of the one conductivity type semiconductor substrate, a gate insulating film provided on the surface of the opposite conductivity type well in the first opening, and at least one of the gate insulating film. A gate electrode provided to extend over the field insulating film so as to partially cover the gate electrode; a reverse conductivity type diffusion layer provided in the reverse conductivity type well in the second opening; A semiconductor device having a first conductor to be connected and a second conductor to be connected to the opposite conductivity type diffusion layer, and exposing the first conductor and the second conductor to a plasma process using the semiconductor device A plasma process application device, An apparatus for evaluating plasma damage, comprising inspecting the gate insulating film after application to a plasma process application apparatus. 8. The apparatus for evaluating plasma damage according to claim 7, wherein the gate insulating film is inspected based on a characteristic of a non-defective rate of the gate insulating film with respect to a distance between the first conductor and the second conductor. An apparatus for evaluating plasma damage. 9. The plasma damage evaluation apparatus according to claim 7, wherein the first conductor and the second conductor are comb-shaped pads, and the antenna effect is obtained by exposing to the plasma process. An evaluation device for plasma damage characterized by a shape that can be played.