JP2000124283A - Identification of defective contact location - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for accurately identifying a defective contact location in a chain of contacts which are formed on a diffused layer connected to each other. SOLUTION: In a method for identifying a defective contact location in a chain of contacts which are electrically connected to each other, aluminum electrodes 5 and an N+ diffused layer 3 provided at upper and lower levels of an interlayer insulating film disposed between the electrodes and the diffused layer are electrically connected through contact plugs 7, lower wiring lines 9 are formed on ones of element isolating regions by which the N+ diffusion layer 3 is separated and which are located in the lower layer of the aluminum electrodes 5, the lower wiring lines 9 and one pad 6a of the contact chain are both grounded, these contacts are irradiated with an electron or ion beam to identify defective one of the contacts, based on a secondary electron image obtained by the radiation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for specifying a defective contact portion of a contact chain in which conductive layers formed above and below an insulating layer are electrically connected through contact holes.

[0002]

2. Description of the Related Art In order to clarify the cause of a contact chain resistance abnormality or a contact opening defect, it is necessary to specify a portion where the resistance abnormality or the opening defect has occurred. As a method for that, SEM (Scanning Electron Micr
Scope) or EB Tester (Electron Beam Tester)
There is a method of irradiating a sample with electrons or ions using a FIB (Focused Ion Beam) device and observing an image of secondary electrons emitted from the surface of the sample to specify a defective portion. As an example, JP-A-5-144901 discloses a FI
There is disclosed a method of detecting a connection failure of a contact chain by observing a potential difference contrast of a secondary electron image using a B apparatus. Hereinafter, the method disclosed in Japanese Patent Application Laid-Open No. H5-144901 will be specifically described.

FIG. 5 shows a view of a contact chain viewed from above.
FIG. 5A is a sectional view taken along line AA of FIG.
In the configuration shown in FIGS. 5A and 5B, an insulating film 131 is formed on a silicon substrate 130, and further thereon,
A contact chain is provided in which conductive patterns 135 and 132 formed above and below the interlayer insulating film 133 are electrically connected through a contact hole 134. Ground one end of this contact chain to FIB
Irradiation is performed and the secondary electron image is observed.

If there is no open part (high resistance part) in the contact chain, charge-up (accumulation of electric charge) by FIB irradiation does not occur, and the observed secondary electron image becomes bright. On the other hand, if there is an open portion (high resistance portion) in a part of the contact chain, no charge-up occurs from the ground-side end of the contact chain to the open portion, so the observed secondary electron image Is bright, but a charge-up occurs between the open end and the other end.
The amount of secondary electrons decreases, and the observed secondary electron image becomes darker. As described above, if there is an open portion (high-resistance portion) in a part of the contact chain, the energy distribution of electrons is different between the ground side and the opposite side. Therefore, it is possible to specify an open portion of the contact chain based on the potential difference contrast.

[0005]

However, the method of specifying a defective portion of a contact chain based on the potential difference contrast of a secondary electron image as described above is somewhat effective in specifying a defective portion of a via chain. However, the following problem occurs in a chain in which a contact is formed in a diffusion layer and connected.

FIG. 6 shows that a contact is formed in the diffusion layer.
An example of a continuous chain, (a) is a contact chain
(B) is a BB diagram of (a) when the component is viewed from above.
It is sectional drawing. In the structure shown in FIG.
100 denotes an element isolation oxide film 101, a P well 102, and N⁺
A diffusion layer 103 is sequentially provided, and an interlayer film 1 is further formed thereon.
04, a plurality of aluminum electrodes 105 and pads 106
a, 106b are provided.
Are connected to each other through the contact plug 107. ⁺diffusion
A chain is formed by being electrically connected to the layer 103.
You. One of the pads 106a is connected to the silicon substrate 100.
Tact is taken.

When an electron beam or an ion beam is irradiated on the above-mentioned contact chain structure, the interlayer film 1
The electric charge is also accumulated (charged up) on the surface of the element isolation region 04, thereby causing the element isolation region (element isolation oxide film 10
1) becomes conductive. Therefore, between the high-resistance contact (open) 108 and the pad 106b, charges leak to the silicon substrate 100 via the N ⁺ diffusion layer 103 and the element isolation oxide film 101 in a conductive state, and a stable potential difference contrast is obtained. Is not obtained.

In addition, since the potential of the interlayer film 104 itself increases due to charge-up, the amount of secondary electrons from the interlayer film 104 becomes extremely large, and the contrast difference of the secondary electron image in the contact chain. Is also difficult to recognize.

In addition to the above problems, in the method of obtaining a potential difference contrast of a secondary electron image by ion irradiation, when heavy ions such as Ga ions are used, the aluminum electrode 105 or the interlayer film 10 is irradiated by ion irradiation.
4 may be sputtered, and their constituent materials may adhere between the aluminum electrodes 105 to cause a short circuit between wirings. Also in this case, it is difficult to obtain the potential difference contrast.

An object of the present invention is to provide a method capable of accurately specifying a defective contact portion of a contact chain in which a contact is formed in a diffusion layer and connected.

[0011]

According to a first aspect of the present invention, a plurality of first conductor patterns and a plurality of diffusion layers formed above and below an interlayer insulating film are formed in contact holes. A contact failure portion of a contact chain that is electrically connected to the plurality of diffusion layers, wherein the plurality of diffusion layers are located in a lower layer of the plurality of first conductive patterns in an element isolation region. A second conductor pattern is formed on the element isolation region, and both the second conductor pattern and one end of the contact chain are grounded, and then irradiated with electrons or ions, and secondary electrons obtained by the irradiation are irradiated. The defective portion is specified based on an image.

According to a second aspect of the present invention, there is provided a contact in a contact chain in which a plurality of first conductive patterns formed above and below an interlayer insulating film and a plurality of diffusion layers are electrically connected via contact holes. In the method for specifying a defective portion, a second conductor pattern is formed between the first conductor patterns on the same layer as the layer on which the first conductor pattern is formed, and the second conductor pattern and the contact are formed. After one end of the chain is grounded, electrons or ions are irradiated, and the defective portion is specified based on a secondary electron image obtained by the irradiation.

A third invention provides a contact chain in which a plurality of first conductive patterns formed above and below an interlayer insulating film and a plurality of diffusion layers are electrically connected through contact holes. A method of irradiating ions with one end thereof grounded and identifying a contact failure portion of the contact chain based on a secondary electron image obtained by the irradiation, further comprising:
Forming the second interlayer insulating film in a predetermined pattern to expose the surface of the contact chain, and then performing the ion irradiation.

(Function) In the first aspect of the present invention, since the second conductor pattern formed on the element isolation region located below the first conductor pattern functions as a field plate, irradiation of electrons or ions is performed. Even if charges are accumulated on the surface of the interlayer insulating film, the element isolation region does not conduct. Therefore, in the first invention, there is no problem that the charge leaks through the element isolation region when the charge-up is performed as in the related art, and a stable potential difference contrast cannot be obtained on the surface of the interlayer insulating film.

In the second invention, since the second conductor pattern having one end grounded is provided between the first conductor patterns, the exposed surface of the interlayer insulating film can be reduced. In addition, charge accumulation on the surface of the interlayer insulating film at the time of charge-up is reduced. Therefore, also in the second invention, similarly to the first invention, the potential difference contrast of the secondary electron image obtained by charge-up becomes clear.

In the third aspect of the present invention, the second interlayer insulating film is opened in a predetermined pattern to expose the contact chain surface, and then the ion irradiation is performed. Therefore, even if the contact chain surface is sputtered, The constituent material does not adhere between the conductor patterns constituting the contact chain and does not cause a short circuit between wirings.

[0017]

Next, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1A and 1B show an embodiment of a contact chain structure applied to the method for specifying a defective contact position according to the present invention, wherein FIG. 1A is a structural view when viewed from above, and FIG.
It is CC sectional drawing of.

In this contact chain structure, an element isolation oxide film 1, a P well 2, and an N ⁺ diffusion layer 3 are sequentially provided on a silicon substrate 10, and a plurality of aluminum electrodes 5, pads 6a and 6b are provided, and the aluminum electrode and the pad are electrically connected to the N ⁺ diffusion layer 3 via the contact plugs 7 respectively to form a chain up to the point shown in FIG. It has the same structure as In this contact chain structure, a lower layer wiring (gate wiring) 9 is further provided on the element isolation oxide film 1 immediately below each aluminum electrode 5, and each lower layer wiring 9 makes contact with the silicon substrate 10 together with the pad 6a. Have been. The lower wiring 9 may have a continuous pattern as shown in FIG. 2, for example, and may be configured so that at least one end is in contact with the silicon substrate 10.

In the above-described contact chain structure, when the aluminum electrode is charged up by irradiating an electron beam or an ion beam, electric charges are accumulated (charged up) also on the surface of the interlayer film 4. Since it functions as a field plate, the element isolation region (element isolation oxide film 1) between the N ⁺ diffusion layers 3 does not conduct due to the charge-up on the surface of the interlayer film 4.

FIG. 3A is a view showing a contrast difference of a secondary electron image when the contact chain shown in FIG. 1 is charged up, and FIG. 3B is a sectional view taken along the line DD of FIG. 3A. 5 shows the state of the orbit of the secondary electrons emitted from the aluminum electrode in FIG. As can be seen from FIGS. 3A and 3B, a bright secondary electron image is observed on the pad 6a (ground) side with respect to the high resistance contact (open) 8 because no charge-up occurs. On the other hand, on the pad 6b side, the aluminum electrode is positively charged by charge-up, so that the emitted secondary electrons are returned to the substrate side and detected.
The amount of secondary electrons decreases, and the observed secondary electron image becomes darker. As described above, the secondary electron distribution differs between the ground side and the opposite side with respect to the high-resistance contact 8, and a clear potential difference contrast can be obtained. Thereby, the position of the high-resistance contact 8 can be accurately specified.

The contact chain structure described above is
It can be manufactured by the following steps.

First, as shown in FIG. 4A, an element isolation oxide film 1 is formed on a silicon substrate 10 and a P well 2 is formed in the same manner as in a known semiconductor manufacturing process.

Subsequently, as shown in FIG.
Isolation oxidation located directly below the aluminum electrodes that make up the
After the lower wiring 9 is formed on the film 1, the space between the element isolation oxide films 1 is formed.
N ⁺The diffusion layer 3 is formed.

Subsequently, as shown in FIG.
After the interlayer film 4 is formed, a contact opening for making contact between the aluminum electrode forming the chain and the N ⁺ diffusion layer 3 is formed, and a contact plug 7 is formed. At this time, a contact between one pad of the chain and the lower wiring 9 and the silicon substrate 10 is simultaneously taken. Finally, an aluminum electrode 5 and pads 6a and 6b are formed.

In the actual analysis of the causes of abnormal contact resistance and defective contact openings, a large number of contact chains are arranged on the wafer surface, and the resistance of each contact chain is measured to identify the defective chain. Then, for the defective chain, a potential difference contrast image is fetched using, for example, an FIB device, and a defective position is specified based on the potential difference contrast image to analyze the cause (for example, contact shape, cross-sectional TEM observation of the interface between the wiring and the substrate). Physical analysis such as).

In the example shown in FIG. 1, the contact is formed in the N ⁺ diffusion layer to form a contact chain. However, the contact is formed in the P ⁺ diffusion layer to form a contact chain. You may do so. In this case, the potential difference contrast of the SEM or SE
An M-type defect inspection device can be used.

Further, in the example shown in FIG. 1 described above, the lower wiring 9 is formed on the element isolation oxide film immediately below the aluminum electrode constituting the chain. Alternatively, an increase in the surface potential of the interlayer film can be reduced by adopting the following configuration. That is, a conductor pattern is formed between the aluminum electrodes on the same layer as the aluminum electrodes constituting the chain, and this is connected to the ground. In this case, by providing the conductor pattern not only between the aluminum electrodes but also around the contact chain,
The increase in the surface potential of the interlayer film can be further reduced.

Further, in the example shown in FIG. 1 described above, the lower wiring 9 is in contact with the silicon substrate 10, but this lower wiring 9 is individually pulled out to apply a predetermined potential. Can obtain the same effect.

Next, in the specific method described above, F
A method for preventing a phenomenon that a constituent material of an aluminum electrode or an interlayer film sputtered by ion irradiation by IB adheres between aluminum electrodes to cause a short circuit between wirings will be described.

After a contact chain is formed in the steps shown in FIGS. 4A to 4C, a second interlayer film is further formed, and the second interlayer film is formed by a contact chain pattern or a similar pattern. An opening is formed in a pattern to expose the aluminum electrode 5 and the pads 6a and 6b. According to this configuration, the surface of the aluminum electrode and the second interlayer film constituting the chain is sputtered by the ion irradiation by the FIB, but the constituent materials adhere between the aluminum electrodes to cause a short circuit between the wirings. Does not occur.

[0032]

According to the present invention configured as described above, even if charges are accumulated on the surface of the interlayer insulating film during charge-up, the element isolation region does not conduct, so that it is clear. Thus, there is an effect that a potential difference contrast of a secondary electron image can be obtained, and a contact failure portion can be accurately specified.

In the present invention, the second conductive pattern is provided between the first conductive patterns.
Since the accumulation of electric charges on the surface of the interlayer insulating film at the time of charge-up is reduced in the case where the conductor pattern is provided, a clear potential difference contrast of the secondary electron image can be obtained as in the above case. Therefore, there is an effect that a defective contact portion can be accurately specified.

In the present invention, in which the second interlayer insulating film is opened in a predetermined pattern to expose the surface of the contact chain and is irradiated with ions, even if the surface of the contact chain is sputtered, the short circuit between the wirings occurs. Therefore, there is an effect that a contact failure portion can be specified more accurately. .

[Brief description of the drawings]

FIGS. 1A and 1B show an embodiment of a contact chain structure applied to a method for identifying a defective contact portion according to the present invention, wherein FIG. 1A is a configuration diagram when viewed from above, and FIG. FIG.

FIG. 2 is a diagram illustrating an example of a lower wiring.

3A is a diagram showing a contrast difference of a secondary electron image when the contact chain shown in FIG. 1 is charged up, and FIG. 3B is a diagram showing a difference between an aluminum electrode and a cross section taken along line DD in FIG. It is a figure which shows the state of the orbit of the emitted secondary electron.

FIGS. 4 (a) to 4 (c) are process diagrams for describing a procedure for manufacturing the contact chain shown in FIG.

FIGS. 5A and 5B are diagrams for explaining the method disclosed in Japanese Patent Application Laid-Open No. H5-144901, wherein FIG. 5A is a view of the contact chain as viewed from above, and FIG. It is.

FIG. 6 is an example of a chain in which contacts are formed and connected to a diffusion layer, where (a) is a configuration diagram when the contact chain is viewed from above, and (b) is a cross-sectional view taken along line BB of (a). is there.

[Explanation of symbols]

Reference Signs List 1 element isolation oxide film 2 P well 3 N ⁺ diffusion layer 4 interlayer film 5 aluminum electrode 6 a, 6 b pad 7 contact plug 8 high resistance contact 9 lower wiring 10 silicon substrate

Claims (7)

[Claims] 1. A contact failure location of a contact chain in which a plurality of first conductive patterns formed above and below an interlayer insulating film and a plurality of diffusion layers are electrically connected through contact holes. In the method, a second conductor pattern is formed on an element isolation region located below the plurality of first conductor patterns in an element isolation region that separates the plurality of diffusion layers. A contact, wherein both the second conductor pattern and one end of the contact chain are grounded and irradiated with electrons or ions, and the defective contact portion is specified based on a secondary electron image obtained by the irradiation. Defective location identification method. 2. The method according to claim 1, wherein the diffusion layer is an N ⁺ diffusion layer, and the secondary electron image is obtained by ion irradiation. 3. The method according to claim 1, wherein the diffusion layer is a P ⁺ diffusion layer, and the secondary electron image is obtained by electron irradiation. 4. A contact failure point of a contact chain in which a plurality of first conductive patterns formed above and below an interlayer insulating film and a plurality of diffusion layers are electrically connected via contact holes. Forming a second conductor pattern between the first conductor patterns on the same layer as the layer on which the first conductor patterns are formed;
The second conductor pattern and one end of the contact chain are both grounded and then irradiated with electrons or ions, and the defective contact portion is specified based on a secondary electron image obtained by the irradiation. How to identify contact failure points. 5. The method according to claim 4, wherein the second conductor pattern is further formed so as to surround the first conductor pattern and grounded. Method. 6. The method according to claim 1, further comprising forming a second interlayer insulating film on the contact chain, wherein the second interlayer insulating film is formed on the contact chain. And irradiating with the ions after exposing the surface of the contact chain by opening a predetermined pattern. 7. A contact chain in which a plurality of first conductor patterns formed above and below an interlayer insulating film and a plurality of diffusion layers are electrically connected via contact holes, one end of which is grounded. Irradiating the ion after the irradiation, and specifying a contact failure portion of the contact chain based on a secondary electron image obtained by the irradiation, further comprising forming a second interlayer insulating film on the contact chain; A method for identifying a defective contact portion, comprising: opening a second interlayer insulating film in a predetermined pattern to expose the surface of the contact chain; and irradiating the ions with the ions.