# Patent

## Title
Semiconductor device including chips with electrically-isolated test elements and its manufacturing method

## Abstract

In a semiconductor device including a semiconductor substrate and an electrode pad formed over the semiconductor substrate, at least one of test element is formed in a region of the semiconductor substrate beneath the electrode pad. The test element is electrically isolated from upper conductive layers outside of the region and the electrode pad.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device including test element group (TEG) elements and its manufacturing method.
2. Description of the Related Art
Generally, in a method for manufacturing a semiconductor device (wafer), TEG elements are formed in the semiconductor device, so that the electrical properties thereof can be evaluated by contacting probes to the TEG elements.
In a first prior art semiconductor device (wafer) (see: JP-2002-313864-A), a semiconductor wafer is divided into product chip areas. Also, TEG elements are formed beneath electrode pads in each of the product chip areas, while test electrode pads are formed in scribe line areas. The TEG elements are electrically connected to the test electrode pads. Therefore, the electrical properties of the semiconductor wafer can be evaluated by contacting probes to the test electrode pads.
In the above-described first prior art semiconductor device (wafer), since the TEG elements are covered by the electrode pads in the product chip areas, a third party including users cannot observe the TEG elements. In addition, after the semiconductor wafer is diced and assembled into chip packages, the test electrode pads in the scribe line areas are scrapped. Therefore, the electrical properties of the semiconductor wafer are never evaluated by a third party including users. Also, since the TEG elements and the test electrode pads do not require additional occupied areas, the integration of the product chips is not affected. Further, since the TEG elements and the test electrode pads are formed simultaneously by the manufacturing steps for the other portions of the product chip areas, the manufacturing cost hardly increases. Still further, since test chip areas for only TEG elements are not included in the semiconductor wafer, the manufacturing steps are not so complex, which also would not increase the manufacturing cost.
In the above-described first semiconductor wafer, however, after the semiconductor wafer is diced and assembled into chip packages, it is impossible for the manufacturer per se to evaluate the electrical properties of the semiconductor wafer. Note that, even after the semiconductor wafer is diced and assembled into the chip packages, the electrical properties of the chip packages are often required to be evaluated under various environments such as temperature environment and humidity environment.
In a second prior art semiconductor device (wafer) (see: JP-9-321104-A), a semiconductor wafer is also divided into product chip areas. Also, TEG elements are formed beneath main electrode pads in each of the product chip areas, and sub electrode pads (test electrode pads) are formed in each of the product chip areas. The TEG elements are electrically connected to the test electrode pads as well as the main electrode pads. Therefore, the electrical properties of the semiconductor wafer can be evaluated by contacting probes to the test electrode pads.
In the above-described second prior art semiconductor wafer, even after the semiconductor wafer is diced and assembled into chip packages, since the test electrode pads are not scrapped, the manufacturer per se can evaluate the electrical properties of the semiconductor wafer. Also, since the TEG elements and the test electrode pads are formed simultaneously by the manufacturing steps for the other portions of the product chips, the manufacturing cost hardly increases. Further, since test chip areas for only TEG elements are not provided in the semiconductor wafer, the manufacturing steps are not so complex, which also would not increase the manufacturing cost.
In the above-described second prior art semiconductor wafer, however, although the TEG elements are covered by the main electrode pads, even when the semiconductor wafer is diced and assembled into chip packages, the test electrode pads are not scrapped. Therefore, a third party including users can easily evaluate the electrical properties of the semiconductor wafer. Also, since the sub electrode pads (test electrode pads) are required in each of the product chip areas, the integration would be negatively affected. Further, bonding wire of the main electrode pads would be short-circuited to the sub electrode pads (test electrode pads).
In a third prior art semiconductor device (wafer), a semiconductor wafer is divided into product chip areas where TEG elements are not formed and test chip areas where various kinds of TEG elements and their test electrode pads are formed.
In the above-described third prior art semiconductor wafer, even after the semiconductor wafer is diced and assembled into chip packages, since test chip packages are obtained, the manufacturer per se can evaluate the electrical properties of the semiconductor wafer. Also, since the TEG elements are not included in the product chip areas, the electrical properties of the semiconductor wafer are never evaluated by a third party including users. Further, since the product chip areas do not require additional occupied areas, the integration of the product chips is not affected.
In the above-described third prior art semiconductor wafer, however, since the manufacturing steps for the product chip areas are different from those for the test chip areas, the manufacturing steps become complex, which would increase the manufacturing cost. Particularly, the result of the test chip areas by chemical mechanical polishing (CMP) steps and etching steps affects the product chip areas. As a result, the properties of the product chips would deteriorate.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a highly-integrated, inexpensive and non-complex semiconductor device where the manufacturer per se can evaluate the electrical properties of product chips while a third party including users cannot evaluate them even after the semiconductor device is diced and assembled into the semiconductor chips.
Another object is to provide a method for manufacturing such a semiconductor device.
According to the present invention, in a semiconductor device including a semiconductor substrate and an electrode pad-formed over the semiconductor substrate, at least one of test element is formed in a region of the semiconductor substrate beneath the electrode pad. The test element is electrically isolated from upper conductive layers outside of the region and the electrode pad. As a result, when the semiconductor device is diced and assembled into semiconductor chips, the manufacturer per se can evaluate the semiconductor device, while a third party including users cannot evaluate the semiconductor device due to the electrical disconnection between the test element and the electrode pad. In this case, since the test element is covered by the electrode pad, a third party cannot find the test element. Also, since the test element does not require additional occupied areas, the integration is not affected. Further, since the test element can be formed by the manufacturing steps for the other portions, the manufacturing cost hardly increases. Still further, since the structure can be the same as that of the test chips except for the electrical connection/disconnection between the test element and the electrode pads, the manufacturing steps would not be complex, which would not increase the manufacturing cost and also the properties would not deteriorate.
Also, at least one circuit element is formed in the above-mentioned region. In this case, the circuit element is electrically connected to one of the upper conductive layers and the electrode pad.
Further, in a method for manufacturing a semiconductor device divided into product chip areas, at least one circuit element and at least one test element are formed in each of the product chip areas. Then, a connection structure is formed in each of the product chip areas. Then, electrode pads are formed in each of the product chip areas. Finally, the product chip areas are diced and assembled into chip packages. In this case, the circuit element is electrically connected through the connection structure to some of the electrode pads, while the test element is formed beneath one of the electrode pads and electrically isolated from the electrode pads without being connected to the connection structure.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be more clearly understood from the description set forth below, with reference to the accompanying drawings, wherein:
FIG. 1 is a plan view illustrating a first embodiment of the semiconductor wafer according to the present invention;
FIG. 2 is a partial enlargement as indicated by X in FIG. 1;
FIG. 3 is a cross-sectional view taken along the line Y-Y in FIG. 2;
FIGS. 4A, 4B and 4C are cross-sectional views for explaining a method for manufacturing the semiconductor wafer of FIG. 1;
FIG. 5 is a cross-sectional view of FIG. 3 where no test element is provided in the product chip area;
FIG. 6 is a plan view illustrating a second embodiment of the semiconductor wafer according to the present invention;
FIG. 7 is a plan view illustrating a third embodiment of the semiconductor wafer according to the present invention.
FIG. 8 is a cross-sectional view illustrating a modification of FIG. 3;
FIGS. 9, 10, 11, 12 and 13 are plan views illustrating modifications of FIG. 2;
FIGS. 14A and 14B are cross-sectional views of modifications of the test elements of FIG. 3 where resistance elements are provided as such test elements; and
FIGS. 15A and 15B are cross-sectional views of modifications of the test elements of FIG. 3 where capacitance elements are provided as such test elements.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, which illustrates a first embodiment of the semiconductor device (wafer) according to the present invention, a semiconductor wafer is divided into a plurality of product chips PC and a plurality of test chips TC. In this case, the number of the product chips PC is much larger than that of the test chips TC.
In FIG. 2, which is a partial enlargement as indicated by X in FIG. 1, the product chip PC and the test chip TC are separated by a scribe line area SL. Electrode pads P1, P2, P3 and P4 are provided on the periphery of the product chip PC, and electrode pads P5, P6, P7 and P8 are provided on the periphery of the test chip TC.
Also, in the product chip PC, a TEG element T1 is formed completely beneath one of the electrode pads such as P3. Similarly, in the test chip TC, a TEG element T2 is formed completely beneath one of the electrode pads such as P6. Note that the arrangement of the TEG elements in the product chips PC is the same as that in the test chips TC, so that the manufacturing steps therefor can be simplified.
In the product chip PC, the TEG element T1 is not electrically connected to any of the electrode pads P1, P2, P3 and P4. In other words, the TEG element T1 is electrically isolated from the electrode pads P1, P2, P3 and P4. Note that the electrode pads P1, P2, P3 and P4 are electrically connected via connection lines C1, C2, C3 and C4 to circuit elements (shown not in FIG. 2, but shown in FIG. 3).
On the other hand, in the test chip TC, the TEG element T2 is electrically connected to some of the electrode pads P5, P6, P7 and P8. For example, note that the electrode pads P5, P7 and P8 are electrically connected via connection lines C5, C7 and C8 to circuit elements (shown not in FIG. 2, but shown in FIG. 3).
In FIG. 3, which is a cross-sectional view taken along the line Y-Y′ in FIG. 2, reference numeral 1 designates a p−-type monocrystalline silicon substrate on which gate electrodes 2 made of polycrystalline silicon or the like are formed via a gate insulating layer (not shown). Also, n+-type impurity diffusion regions 3 are formed in self-alignment with the gate electrodes 2. As a result, in the product chip PC, a circuit element CE1 is formed by one MOS transistor and a TEG element T1 is formed by one MOS transistor. Similarly, a TEG element T2 is formed by one MOS transistor and a circuit element CE2 is formed by one MOS transistor.
Also, an insulating layer 4 is formed where contact structures 4a are formed and reach the impurity regions 3. Connection layers 4b are formed on the contact structures 4a. 
Further, an insulating layer 5 is formed where through structures 5a are formed and reach the gate electrodes 2 and the connection layers 4b. Connection layers 5b are formed on the through structures 5a. 
Additionally, an insulating layer 6 is formed where through structures 6a are formed and reach the connection layers 5b. Electrode pads P1, P2, . . . , P8 are formed on the through structures 6a and the insulating layer 6.
Finally, a passivation layer 7 is formed and perforated to expose the electrode pads P1, P2, . . . , P8, thus completing the semiconductor wafer of FIG. 1.
In FIG. 3, the electrode pad P2 is connected via a connection line C2 formed by the through structure 6a, the connection layer 5b and the through structure 5a to the gate electrode 2 of the circuit element CE1. The electrode pad P3 is connected via a connection line C3 (not shown) to a circuit element (not shown). The electrode pad P4 is connected via a connection line C4 (not shown) to a circuit element (not shown). The electrode pad P5 is connected via a connection line C5 formed by the through structure 6a, the connection layer 5b, the through structure 5a, the connection layer 4b and the contact structure 4a to the impurity region 3 of the TEG element T2. The electrode pad P6 is not electrically connected to any element. The electrode pad P7 is connected via a connection line C7 formed by the through structure 6a, the connection layer 5b, the through structure 5a, the connection layer 4b and the contact structure 4a to the impurity region 3 of the TEG element T2. The electrode pad P8 is connected via a connection line C8 formed by the through structure 6a, the connection layer 5b, the through structure 5a, the connection layer 4b and the contact structure 4a to the gate electrode 2 of the TEG element T2.
A method for manufacturing the semiconductor wafer of FIGS. 1, 2 and 3 will be explained next in detail with reference to FIGS. 4A, 4B and 4C as well as FIG. 3.
First, referring to FIG. 4A, a p−-type monocrystalline silicon substrate 1 is thermally oxidized to form a gate insulating layer (not shown) made of silicon dioxide. Then, gate electrode layer made of polycrystalline silicon or the like is deposited on the gate insulating layer, and is patterned by a photolithography and etching process to form gate electrodes 2. Then, n-type impurities are implanted and diffused into the silicon substrate 1 in self-alignment with the gate electrodes 2 to form n+-type impurity diffusion regions 3 which serve as source and drain regions of MOS transistors. Then, an insulating layer is deposited on the entire surface, and contact holes are perforated therein. Then, contact structures 4a are buried in the contact holes. Then, a conductive layer is deposited on the entire surface and is patterned by a photolithography and etching process to form connection layers 4b on the contact structures 4a. 
Next, referring to FIG. 4B, an insulating layer 5 is deposited on the entire surface, and throughholes are perforated therein. Then, through structures 5a are buried in the throughholes. Then, a conductive layer is deposited on the entire surface, and is patterned by a photolithography and etching process to form connection layers 5b on the through structures 5a. 
Next, referring to FIG. 4C, an insulating layer 6 is deposited on the entire surface, and throughholes are perforated therein. Then, through structures 6a are buried in the throughholes. Then, a conductive layer is deposited on the entire surface and is patterned by a photolithography and etching process to form electrode pads P1, P2, . . . , P8 on the through structures 6a. 
Next, referring to FIG. 3, a passivation layer 7 is deposited on the entire surface, and is perforated to expose the electrode pads P1, P2, . . . , P8.
Finally, the product chips PC and the test chips TC are diced and assembled into chip packages where wires are bonded between the electrode pads P1, P2, . . . , P8 and external leads of the packages.
In FIGS. 3, 4A, 4B and 4C, the contact structures 4a and the connection layers 4b are provided for the TEG element T1 of the product chip PC and the TEG element T2 of the test chip TC. On the other hand, the through structures 5a, the connection layers 5b and the through structures 6a are not provided for the TEG element T1 of the product chip PC, while the through structures 5a, the connection layers 5b and the through structures 6a are provided for the TEG element T2 of the test chip TC. As a result, the TEG element T1 of the product chip PC+ is electrically isolated from the electrode pads thereof. On the other hand, the TEG element T2 Of the test chip TC is electrically connected to some of the electrode pads thereof. Also, the manufacturer per se can evaluate the semiconductor wafer by testing the TEG element T2 of the test chip TC, while a third party including users cannot evaluate the semiconductor device (in this case, the product chip PC) due to the electrical isolation of the TEG element T1 and the electrode pads. In this case, since the test element T1 is covered by the electrode pad, the third party cannot find the TEG element T1 of the product chip PC. Also, since the TEG element T1 is provided beneath the electrode pad P3, which does not require additional occupied areas, the integration of the product chip PC is not affected. Further, since the TEG element T1 can be formed by the manufacturing steps for the other portions of the product chip PC except for the through structures 5a, the connection layers 5b and the through structures 6a, the manufacturing cost hardly increases. Still further, since the structure of the product chips can be the same as that of the test chips except for the electrical connection/disconnection between the TEG element T1 and the electrode pads, the manufacturing steps would not be complex, which would not increase the manufacturing cost and also the properties of the product chip PC would not deteriorate. For example, as illustrated in FIG. 5, if the TEG element T1 is not provided in the product chip PC, the flattability characteristics of the insulating layers 5 and 6 deteriorate due to the CMP process, the etching process and the like, so that the properties of the product chip PC would deteriorate.
In FIG. 6, which illustrates a second embodiment of the semiconductor device (wafer) according to the present invention, a semiconductor wafer is divided into a plurality of product chips PC with no test chip. Each of the product chips PC is the same as those of FIG. 1.
In FIG. 7, which illustrates a third embodiment of the semiconductor device (wafer) according to the present invention, a semiconductor wafer is divided into a plurality of test chips TC with no product chip. Each of the test chips TC is the same as those of FIG. 1.
Note that, in an actual wafer manufacturing process, one or more lots each formed by a plurality of semiconductor wafers are processed by a batch process. Therefore, if each lot is formed by a plurality of semiconductor wafers as illustrated in FIG. 6 and one semiconductor wafer as illustrated in FIG. 7, the properties of the product chips PC of the semiconductor wafers as illustrated in FIG. 6 would not deteriorate due to the absence of test chips TC, while the properties of the product chips PC of the semiconductor wafers of FIG. 6 can be evaluated by testing the test chips TC of the semiconductor wafer of FIG. 7.
In the above-described embodiments, although the through structures 5a and the connection layers 5b are not provided for the TEG element T1 of the product chip PC, the through structures 5a and the connection layers 5b can be provided for the TEG element T1 of the product chip PC as illustrated in FIG. 8, thus further improving the flattability characteristics of the semiconductor wafer.
In the above-described embodiments, although the TEG elements T1 and T2 are formed completely beneath the electrode pads P3 and P6, respectively, the TEG elements T1 and T2 can be formed partly beneath the electrode pads P3 and P6, respectively, as illustrated in FIG. 9. Even in this case, a third party including users can hardly find the TEG elements T1 and T2 due to the presence of the insulating layers 5 and 6. Also, if there is a space around the electrode pads, the TEG elements T1 and T2 can be provided in the periphery of the electrode pads T3 and T6 as illustrated in FIG. 10. Even in this case, a third party including users can hardly find the TEG elements T1 and T2 due to the presence of the insulating layers 5 and 6.
In the above-described embodiments, although only one TEG element is provided in each of the chips, a plurality of TEG elements each for one of the electrode pads can be provided as illustrated in FIG. 11. Note that the connection lines for the TEG elements T5, T7 and T8 are omitted to simplify the description. In this case, the size of the source/drain regions, the gate width and the gate length of one TEG element are different from those of the other TEG elements, thus carrying out various kinds of test operations. Also, as illustrated in FIG. 12, if there is a large-sized electrode pad such as P4 or P5 where a plurality of TEG elements can be formed, a plurality of TEG elements such as T1, T2 and T3 and T4, T5 and T6 are formed beneath the electrode pads P4 and P5. Note that, in the TEG elements T4, T5 and T6 of FIG. 12, the gates are connected by a connection line C8 to the electrode pad P8, and the sources are connected by a connection line C7 to the electrode pad P7. Also, in the TEG element T6, the drain is connected via connection line C6 to the electrode P6. The drains of the TEG elements T4 and T5 are connected by connection lines to the other electrode pads; however, such connection lines are omitted to simplify the description. Even in this case, the size of the source/drain regions, the gate width and the gate length of one TEG element are different from those of the other TEG elements, thus carrying out various kinds of test operations.
Further, when the fine structure of elements has been developed while the accuracy of manufacturing equipment such as bonding equipment has been not so improved, electrode pads may be much larger than circuit elements including TEG elements as shown in FIG. 13, where the electrode pads P4 and P5 of FIG. 12 are much larger. In this case, circuit elements CE1, CE2 and CE3 as well as the TEG elements T1, T2 and T3 are provided beneath the electrode pad P4 and circuit elements CE4, CE5 and CE6 are provided beneath the electrode pad P5.
Additionally, in the above-described embodiments, the TEG elements can be formed of other active elements such as bipolar transistors, or passive elements such as resistance elements or capacitance elements. For example, as illustrated in FIGS. 14A and 14B, the TEG elements T1 and T2 are constructed by resistance elements formed by the connection layers 4b. On the other hand, as illustrated in FIGS. 15A and 15B, the TEG elements T1 and T2 are constructed by capacitance elements formed by the layers 2 and 4b and the insulating layers 4 therebetween.

## Claims

1. A semiconductor device, comprising:
a semiconductor substrate;
an electrode pad of a plurality of electrode pads formed over said semiconductor substrate;
at least one test element formed in a region of said semiconductor substrate beneath said electrode pad, said test element being electrically isolated from any of the electrode pads that are disposed outside of said region, and from said electrode pad; and
at least another test element formed beneath another electrode pad of the plurality of electrode pads in said semiconductor substrate,
wherein said another electrode pad is electrically isolated from any element in said semiconductor device.

2. The semiconductor device as set forth in claim 1, wherein said semiconductor device further comprises at least one circuit element formed in said region, and
wherein said at least one circuit element is electrically connected to a group of said electrode pads disposed outside of said region, and to said electrode pad.

3. The semiconductor device as set forth in claim 1, wherein said test element is arranged completely beneath said electrode pad.

4. The semiconductor device as set forth in claim 1, wherein said test element is arranged partly beneath said electrode pad.

5. The semiconductor device as set forth in claim 1, wherein said test element is arranged in a periphery of said electrode pad.

6. The semiconductor device as set forth in claim 1, wherein said test element comprises one of a transistor element, a resistance element and a capacitance element.

7. A semiconductor device, comprising:
a semiconductor substrate;
an electrode pad of a plurality of electrode pads formed over said semiconductor substrate;
at least one test element formed in a region of said semiconductor substrate beneath said electrode pad;
at least one circuit element formed in said region, and
at least another test element formed beneath another electrode pad of the electrode pads in said semiconductor substrate,
wherein said at least one test element is electrically isolated from any of the electrode pads that are disposed outside of said region, and from said electrode pad,
wherein said at least one circuit element is electrically connected to a group of said electrode pads that is disposed outside of said region, and
wherein said another electrode pad is electrically isolated from any element in said semiconductor device.

8. The semiconductor device as set forth in claim 1,
wherein a group of said plurality of electrode pads is electrically connected to said at least one circuit element via a plurality of connection lines.

9. The semiconductor device as set forth in claim 1, wherein an area between said electrode pad and said test element comprises a plurality of insulating layers rather than a through structure.

10. The semiconductor device as set forth in claim 7,
wherein said group of said plurality of electrode pads is electrically connected to said at least one circuit element via a plurality of connection lines.