JP3185876B2 - Method for inspecting contact opening of semiconductor 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 for inspecting a contact opening of a semiconductor device for inspecting whether the bottom of a contact reaches a semiconductor substrate after contact etching.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have become more highly integrated and higher in density, devices have become finer, and it has become difficult to inspect defective portions. For example, in the visual inspection of a microscope immediately after fine contact etching, it is difficult to perform an aperture inspection to determine whether the bottom of the contact has reached the silicon substrate. It has been. It is also necessary to analyze the shape of a defective contact in order to determine the cause of the contact failure.

A conventional method for inspecting a contact opening of a semiconductor device will be described with reference to FIG.

In FIG. 6, an interlayer film 7 is formed on a silicon substrate 70.
1 shows the state of the wafer after the contacts 72 to 75 have been opened so as to reach the silicon substrate 70 in the interlayer film 71 and have been formed. Here, the contact 74
Has a defective opening and does not reach the silicon substrate 70.

In the conventional method for inspecting a contact opening of a semiconductor device, first, primary electrons are irradiated on the wafer surface. Then, the surface potential of the interlayer film 71 increases. However, if the contact is normally opened to the silicon substrate 70, a leak current flows into the silicon substrate 71, and the potential of the peripheral portion of the contact on the surface of the interlayer film 71 decreases. However, when the contact is not normally opened to the silicon substrate 70, the potential of the peripheral portion of the contact on the surface of the interlayer film 71 does not decrease and remains as it is.

[0006] Since a difference is generated in the potential of the surface of the interlayer film 71 as described above, a difference also occurs in the energy distribution of secondary electrons emitted therefrom. In the secondary electron detection system,
An energy filter is provided, and the amount of detected electrons changes according to the energy distribution. This is called a potential difference contrast. By comparing the amount of electrons with a neighboring contact, the position of the contact with the poor opening can be specified.

In this conventional method for inspecting a contact opening of a semiconductor device, electric charges are supplied by irradiating primary electrons. Therefore, the electric potential of the electric charges is determined when the supply of electric charges to the sample and the leakage current are balanced. This means that the potential of the sample surface is being measured. When electrons are irradiated on the sample, the amount of secondary electrons depends on the surface condition of the sample, the amount of carbon film attached to the sample during electron beam irradiation, the degree of vacuum in the apparatus, irradiation history, irradiation conditions, etc. , Are affected in various ways. Further, the amount of secondary electrons not only differs greatly depending on the measurement conditions of the detection system, but also often the energy resolution of the device itself is not good. The measured value has a correlation with the potential, but the relationship is not clear.

[0008] Therefore, it is not a method of inspecting defects by comparison in the neighborhood. When a standard value (criterion) for determining whether or not the contact has been opened is required, it cannot be practically applied.

Since the rise and measurement of the potential are basically performed by one-electron irradiation, a method using a leak current cannot be used.

Further, when the current amount is increased to increase the inspection speed, a wafer with a resist cannot be inspected.

Further, as an inspection method similar to the method of inspecting a contact opening of a semiconductor device, there is a method of specifying a pinhole position of an oxide film by surface potential measurement as shown in FIG.

This method is a method for inspecting whether an oxide film 61 formed on a silicon substrate 60 has a pinhole 62 or not.

In this method, as shown in FIG.
First, charges are supplied to the surface of the oxide film 61 by corona discharge. In the portion where the pinhole 62 exists, the charge flows in the direction of the silicon substrate 60, so that the potential of the oxide film 61 near the pinhole 62 becomes lower than the potential of other regions. Then, as shown in FIG. 7B, the surface potential of the oxide film 61 is measured by the Kelvin probe method using the plate electrode 63 to measure the potential distribution on the entire surface of the wafer. At a certain portion of the pinhole 62, the potential is measured low, so that the position of the pinhole 62 can be specified.

However, in the semiconductor device in which the contact as shown in FIG. 6 is formed, the region where the potential rises due to the occurrence of the defective opening is limited to only a very narrow region near the defective opening contact. Therefore, when this conventional method is applied to a very dense, fine contact opening inspection, since the shape of the plate electrode 63 is large, there is no spatial resolution enough to measure the peripheral potential of one contact. The location of the bad contact cannot be specified. Further, since the plate electrode 63 having a larger area than the contact diameter is used, the S
/ N is not good. Further, since it is not possible to measure each contact having a fine structure, defect inspection cannot be performed.

[0015]

The above-described conventional method for inspecting a contact opening of a semiconductor device has the following problems.

(1) In the method of irradiating the surface of the wafer with primary electrons and inspecting the contact opening based on the amount of secondary electrons emitted, the value obtained varies greatly depending on conditions and is compared with a reference value. And high resolution cannot be obtained.

(2) When the surface potential measurement method using corona discharge is used for the contact opening inspection, good S / N data cannot be obtained, and the position of a poorly-opened contact cannot be specified.

An object of the present invention is to provide a method for inspecting a contact opening of a semiconductor device, which can easily perform a high-resolution contact opening inspection and can easily specify the position of a defective contact.

[0019]

In order to achieve the above object, a method for inspecting a contact opening of a semiconductor device according to the present invention comprises:
A contact opening inspection method for a semiconductor device for inspecting a plurality of contacts formed by etching, wherein the surface of the pattern provided with the plurality of contacts is charged using corona discharge, and after a predetermined time elapses Then, the position of the poorly-opened contact is detected by measuring the surface potential of the region near each contact in the pattern and comparing the obtained surface potential value with the surface potential of the region near the other contact.

In the present invention, first, the surface of the pattern provided with the contacts is charged using corona discharge,
Wait for a certain time. Then, in the region near the contact of the normal opening, the potential is lowered by the leakage current flowing through the semiconductor substrate via the normal contact, but in the region near the contact of the defective opening, the potential is not so low because the leakage current is small. . In the present invention, the position of the poorly-opened contact is specified by measuring the potential difference generated by this. Therefore, the position of the poorly-opened contact can be easily specified.

According to another aspect of the present invention, there is provided a method of inspecting a contact opening of a semiconductor device for inspecting a plurality of contacts formed by etching, wherein the plurality of contacts are provided. The surface of the pattern is charged to a predetermined constant potential using corona discharge, and after a predetermined time has elapsed, the surface potential of the area near each contact in the pattern is measured and obtained. By comparing the obtained surface potential value with a preset reference value, detection of a defective opening contact, measurement of a remaining film amount of the defective opening contact, and estimation of an overetch amount are performed.

According to another aspect of the present invention, there is provided a method of inspecting a contact opening of a semiconductor device for inspecting a plurality of contacts formed by etching, wherein the plurality of contacts are provided. The surface of the pattern is charged to a predetermined constant potential using corona discharge, the time dependence of the surface potential of the area near each contact in the pattern is measured, and the obtained surface potential Based on the time dependency, detection of a defective opening contact, measurement of a remaining film amount of the defective opening contact, and estimation of an overetch amount are performed.

In another method for inspecting a contact opening of a semiconductor device according to the present invention, the surface potential is measured by using a scanning surface potential microscope.

In the present invention, since the surface potential is measured with a high spatial resolution, it is possible to easily detect the position of a poorly-opened contact.

In another contact hole inspection method for a semiconductor device according to the present invention, the probe electrode of the scanning surface potential microscope has a shape corresponding to the arrangement of the plurality of contacts.

According to the present invention, the surface potential of only the area around the contact can be measured, so that the S / N of the measurement can be improved.

[0027]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

(First Embodiment) A method for inspecting a contact opening of a semiconductor device according to a first embodiment of the present invention will be described with reference to FIG.

First, an interlayer film 11 is deposited on a silicon substrate 10, a contact pattern is formed using a resist 12, and then contacts 13 to 16 are formed by plasma etching. This wafer may be a test pattern TEG (test element group) for contact opening inspection, or an actual product.

Next, as shown in FIG. 1A, charges are supplied onto the wafer by corona discharge. In the portion where the contact is sufficiently opened, the charge supplied to the surface of the resistor 12 decreases due to the leak current toward the silicon substrate 10, so that the surface potential in the contact peripheral region decreases. On the other hand, when there is a residual film of the interlayer film 11 at the contact bottom,
Since the leak current is very small, the potential in the region around the contact hardly drops. (FIG. 1B) Then, as shown in FIG. 1C, the surface potential of the contact formation region is measured by a scanning surface potential microscope (Kelvin probe force microscope). This measurement is performed after waiting for several minutes until a leak current occurs and a potential difference occurs for several minutes after corona discharge.

The scanning surface potential microscope uses the probe electrode 17 so that the surface potential of the sample can be measured in a non-contact manner. The probe electrode 17 includes a needle 17a and a beam 17b formed of a conductive material. The spatial resolution depends on the shape of the tip of the needle 17a, but has a performance of about 0.1 μm, and the potential resolution has a performance of about 10 meV at the actual measurement level.

The method of using a scanning surface potential microscope for contact opening inspection is not always common and cannot be easily inferred from conventional techniques. This is because defect detection can be performed with sufficient accuracy only by a combination of supplying charges by corona discharge.

In the method of the present embodiment, the measurement of the surface potential is performed in a non-contact manner, so that a stable measurement can be performed. Also, the surface potential is obtained as a measured value. FIG. 2 shows the measured values of the surface potential. In FIG. 2, the solid line indicates the surface potential immediately after corona discharge has occurred, and the broken line indicates the measured value of the surface potential after a potential difference has occurred due to the leakage current generated several minutes later.

Referring to FIG. 2, the surface potential is about 10 V in a region where no contact is formed. The potential around the open contact is reduced to about several volts or less, but for a contact that is not sufficiently opened, the potential hardly changes to about 10-8 V. Therefore, the position of the contact having the opening defect can be detected from the difference in the potentials (the difference between the potentials of the surrounding contacts is compared as in a normal defect inspection apparatus). In addition, since the potential gradually decreases due to the leak current even on a normal resist, the charge is supplied again by corona discharge after a certain period of time.

(Second Embodiment) Next, a method for inspecting a contact opening of a semiconductor device according to a second embodiment of the present invention will be described.

In this embodiment, the corona discharge conditions are optimized so that the surface potential of the wafer becomes a reference value. Alternatively, directly measure the potential of the area where the pattern is not formed immediately after corona discharge, and adjust the potential so that it becomes a constant value in each inspection by supplying a reverse charge that adds corona discharge. I do. Charge supply by corona discharge may be performed only in the measurement pattern area. When measuring the TEG region for opening check of a product, the corona discharge region may be narrowed to that region.

Since the surface potential in the initial state at the start of the inspection is constant for each inspection, the surface potential of the wafer is measured after a certain standby time, and it is determined whether the potential is higher or lower than a reference value. Thus, it can be determined whether the contact has been opened normally.

FIG. 3A is a diagram showing the waiting time dependency of the surface potential when the contact opening is normal, and FIG. 3B is a diagram showing the contact opening failure (remaining film 10n).
FIG. 9 is a diagram showing the waiting time dependency of the surface potential in the case of m).

This reference value is determined in advance by performing cross-sectional observation after the inspection and measuring the remaining film. In a product wafer, there is a difference in structure such as whether a diffusion layer is formed on the base and whether a PN junction exists or not for each product and each region to be inspected. Therefore, it is necessary to determine corona discharge conditions and measurement conditions in advance. There is.

In a product wafer, if a diffusion layer is formed as a base, the contact resistance value changes depending on the amount of overetching of the diffusion layer. Also, when the depth of the overetch changes, the amount of leak current changes greatly.

When the overetch progresses greatly, the contact bottom penetrates the diffusion layer, so that the amount of leak current decreases. Therefore, the potential is slightly higher than in the case where the potential remains in the diffusion layer.

Therefore, the relationship between the amount of overetching and the surface potential is measured in advance, and the surface potential around the contact is measured to determine whether the contact bottom stays in the diffusion layer or penetrates the diffusion layer. The amount of overetch can be estimated.

Also, by directly measuring the time dependence of the potential,
Based on the tendency, the remaining film amount and the overetch amount may be estimated.

FIG. 4 is a diagram showing the change in the waiting time dependency of the surface potential depending on the remaining film amount and the change in the waiting time characteristic of the surface potential depending on the overetch amount.

In the contact opening inspection method according to the present embodiment, it is preferable to select the side on which the leakage current increases due to the underlying structure as the electric charge given to the wafer surface by corona discharge. For example, in the N ⁺ diffusion layer / P well, it is preferable to select a negative charge that forward biases the PN junction.

(Third Embodiment) Next, a method for inspecting a contact opening of a semiconductor device according to a third embodiment of the present invention will be described.

In the first and second embodiments, when the value of the surface potential to be measured requires an accuracy of 1 V or less,
The measured value obtained depends on the shape and state of the needle tip, and also on the value of the voltage drop inside the measuring circuit. Therefore, a more accurate measurement value can be obtained by measuring the offset value with a standard sample such as a gold thin film each time measurement is performed.

In the case of the second embodiment, it is not necessary to measure the potential of the peripheral portion of each contact, but it is necessary to improve the measurement sensitivity and S / N.

In the conventional potential measuring device shown in FIG. 7, since the measurement was performed using the plate electrode 63, the SN was not good.

Therefore, in the present embodiment, the apparatus is configured to measure the potential near the contact opening using the probe electrode 19 having the same period and the same shape as the periodically provided contact pattern. . Probe electrode 1
In order to improve the parallelism of 9, insulating columns 18 a and 18 b are provided at both ends. As a result, only the potential in the vicinity of the contact can be selectively measured, so that the obtained value is the sum from many contacts,
The SN is improved, and a contact opening inspection can be performed with high accuracy. In the present embodiment, it is necessary to align the positions of the protruding probe electrode 19 and the contacts 13 to 16 so that the obtained value is maximized.

[0051]

As described above, the present invention has the following effects. (1) The position of the poorly-opened contact can be easily specified. (2) The residual film amount at the contact bottom can be measured and the overetch amount can be estimated.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a contact opening inspection method for a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating an operation of the contact opening inspection method for the semiconductor device of FIG. 1;

FIG. 3 is a diagram showing the waiting time dependency of the surface potential when the contact opening is normal (FIG. 3A), and the waiting time dependency of the surface potential when the contact is poorly opened (remaining film 10 nm). FIG. 3B is a diagram showing the characteristics (FIG. 3B).

FIG. 4 is a diagram showing a change in the waiting time dependency of the surface potential depending on the remaining film amount and a change in the waiting time characteristic of the surface potential depending on the overetch amount.

FIG. 5 is a diagram for explaining a contact opening inspection method for a semiconductor device according to a third embodiment of the present invention.

FIG. 6 is a view for explaining a conventional contact opening inspection method for a semiconductor device.

FIG. 7 is a diagram for explaining a method of specifying a pinhole position of an oxide film by measuring a surface potential by corona discharge.

[Explanation of symbols]

 Reference Signs List 10 silicon substrate 11 interlayer film 12 resistor 13-16 contact 17 probe electrode 17b conductive beam 17a conductive needle 18a, 18b support 19 probe electrode 60 silicon substrate 51 resist 52 interlayer film 60 silicon substrate 61 oxide film 62 pinhole 63 plate electrode 70 silicon substrate 71 interlayer film 72-75 contact

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/66 H01L 21/28 H01L 21/302

Claims (9)

(57) [Claims] 1. A contact opening inspection method for a semiconductor device for inspecting a plurality of contacts formed by etching, wherein a surface of a pattern provided with the plurality of contacts is charged using corona discharge. After a lapse of a predetermined time, the surface potential of the area near each of the contacts in the pattern is measured, and the obtained surface potential value is compared with the surface potentials of the areas near the other contacts. A contact opening inspection method for a semiconductor device for detecting a position. 2. A method for inspecting a contact opening of a semiconductor device for inspecting a plurality of contacts formed by etching, wherein a surface of a pattern provided with the plurality of contacts is predetermined using corona discharge. After a predetermined period of time, the surface potential of the area near each contact in the pattern is measured, and the obtained surface potential value is set to a preset reference value. A method for inspecting a contact opening of a semiconductor device, which detects a defective opening contact by comparing with the method of 3. A method for inspecting a contact opening of a semiconductor device for inspecting a plurality of contacts formed by etching, wherein a surface of a pattern provided with the plurality of contacts is predetermined using a corona discharge. After a predetermined period of time, the surface potential of the area near each contact in the pattern is measured, and the obtained surface potential value is set to a preset reference value. A method for inspecting a contact opening of a semiconductor device, wherein the amount of a remaining film of a contact with a defective opening is measured by comparing with the method of FIG. 4. A method for inspecting a contact opening of a semiconductor device for inspecting a plurality of contacts formed by etching, wherein a surface of a pattern provided with the plurality of contacts is predetermined using corona discharge. After a predetermined period of time, the surface potential of the area near each contact in the pattern is measured, and the obtained surface potential value is set to a preset reference value. A contact opening inspection method for a semiconductor device, wherein an over-etch amount of the contact is estimated by comparing with the above. 5. A method for inspecting a contact opening of a semiconductor device for inspecting a plurality of contacts formed by etching, wherein a surface of a pattern provided with the plurality of contacts is predetermined using corona discharge. Of the semiconductor device that is charged to a given constant potential, measures the time dependence of the surface potential of a region near each of the contacts in the pattern, and detects a poorly-opened contact from the time dependence of the obtained surface potential. Contact opening inspection method. 6. A contact opening inspection method for a semiconductor device for inspecting a plurality of contacts formed by etching, wherein a surface of a pattern provided with the plurality of contacts is predetermined using corona discharge. Charged to a given potential, and measures the time dependency of the surface potential of the area near each of the contacts in the pattern, and measures the remaining film amount of the poorly-opened contact from the obtained time dependency of the surface potential. Inspection method for a contact opening of a semiconductor device. 7. A contact opening inspection method for a semiconductor device for inspecting a plurality of contacts formed by etching, wherein a surface of a pattern provided with the plurality of contacts is predetermined using corona discharge. Charged to a predetermined potential, measuring the time dependence of the surface potential of the area in the vicinity of each contact in the pattern, and estimating the overetch amount of the contact from the time dependence of the obtained surface potential. Method for inspecting contact opening of semiconductor device. 8. The method according to claim 1, wherein the measurement of the surface potential is performed using a scanning surface potential microscope. 9. The method according to claim 8, wherein the probe electrode of the scanning surface potential microscope has a shape corresponding to the arrangement of the plurality of contacts.