Semiconductor device having conductor with aperture

Abstract: Formed over a semiconductor substrate (1) having an element (Q) is a conductor (6) which has a hollow (6a) opposing the element.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a semiconductor device having multi-layer connections. Description of the Related Art Recently, development of apparatuses used in the evaluation and analysis of semiconductor devices has advanced remarkably. An electron beam tester has been developed to expose an element of a semiconductor device to a beam of electrons, so that the operational state of the element can be evaluated by detecting secondary electrons depending upon the potential at the element. Also, an apparatus has been developed to detect photons due to the current concentration in a local breakdown portion of a MOS transistor, thus detecting such a breakdown portion. On the other hand, a large number of circuit elements are formed on a semiconductor substrate, and are interconnected with each other by connection layers thereby to carry out desired functions or operations. A multi-level connection structure is commonly used to increase the density of the connection layers. This means, however, that elements are often covered by a connection layer or a conductive layer made of aluminium or the like, and in this case, a beam of electrons are shut off by the conductor layer. Therefore, the beam of electrons cannot reach such elements, and likewise, the generated secondary electrons and photons cannot reach the surface of the device. As a result, it is impossible to effectively operate the above-mentioned evaluation/analysis apparatus for the elements covered by the conductive layer. This will be later explained in detail. JP-A-4075370 discloses a power-supply wiring method for large scale interpreted circuits. According to this document a conductive wiring layer forms a plurality of longitudinal and transverse conductor strips or wires each having a predetermined width. Most of these conductor strips are so arranged that they do not cover any of the circuit elements which are formed in the block regions. Some of the conductor strips are wires, however, and extend over regions of the chip where circuit elements are supposed to be formed. This means that in the LSI-circuit disclosed in this document a circuit element is either located in an area laterally offset from a conductor strip and not covered by the conductor strip, or the circuit element is located under a conductor strip in which case it is covered by the metallic conductor strip and shielded against electron beam or photon inspection. JP-A-4162546 discloses a method for modifying an integrated circuit device for enabling to analyse an underlying wiring. For this purpose a hole is formed in the insulating layer above the underlying wiring so that the insulating layer and a portion of an overlying conductor is removed. The severed ends of the overlying conductor are reconnected using a conductor formed to pass around said hole. SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor device having an element covered by a conductor, which can be easily tested by the above-mentioned estimation/analysis apparatuses. This object is achieved by a semiconductor device according to claim 1. The dependent claims are related to further advantageous aspects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more clearly understood from the description as set forth below, in comparison with the prior art, with reference to the accompanying drawings, wherein: Fig. 1 is a plan view illustrating a part of a prior art semiconductor device; Fig. 2A is an enlarged plan view of the device of Fig. 1; Fig. 2B is a cross-sectional view taken along the line B-B of Fig. 2A; Fig. 3A is a plan view illustrating a first embodiment of the semiconductor device according to the present invention; Fig. 3B is a cross-sectional view taken along the line B-B of Fig. 3A; Fig. 4A is a plan view illustrating a second embodiment of the semiconductor device according to the present invention; Fig. 4B is a cross-sectional view taken along the line B-B of Fig. 4A; Fig. 5A is a plan view illustrating a third embodiment of the semiconductor device according to the present invention; and Figs. 5B is a cross-sectional view taken along the line B-B of Fig. 5A. DESCRIPTION OF THE PREFERRED EMBODIMENTS Before the description of embodiments of the present invention, a prior art semiconductor device will be explained with reference to Figs. 1, 2A and 2B. In Fig. 1, which illustrates a prior art semiconductor device, this device includes a semiconductor substrate 1 on which a conductive layer 6 for a power supply voltage V cc is formed. The conductive layer 6 is located at the periphery of the semiconductor substrate 1, to apply the voltage V cc to the circuit elements (not shown) formed on the semiconductor substrate 1. Since the conductive layer 6 is wide, some circuit elements such as a MOS transistor Q is formed under the conductive layer 6. In this case, the MOS transistor Q is connected via signal conductive layers 11 to another internal circuit element (not shown). The proximity of the transistor Q is explained with reference to Figs. 2A and 2B which are plan and cross-sectional views, respectively. Formed over the semiconductor substrate 1 such a P - -type monocrystalline silicon substrate is a gate electrode 2 made of polycrystalline silicon. Also, N + -type impurity diffusion regions 3 and 3' serving as source and drain regions are formed in alignment with the gate electrode 2. Further, conductive layers 4 and 4' made of aluminium are connected via contact holes 5 and 5' to the impurity diffusion regions 3 and 3', respectively, and a conductive layer 4'' made of aluminium is connected via a contact hole 5'' to the gate electrode 2. Thus, the MOS transistor Q of Fig. 1 is obtained. Further, the conductive layer 6 made of aluminium for a power supply voltage such as V cc is formed over the MOS transistor Q with an isolation layer (insulating layer) 20 therebetween, thus reducing the size of a chip area. Note that the width of the conductive layer 6 is about 50 to 100 µm to suppress the voltage drop of the power supply voltage V cc due to the resistance value of the conductive layer 6. In the device of Figs. 2A and 2B, however, as explained above, a beam of electrons being projected toward the MOS transistor Q would be shut off by the conductive layer 6, and accordingly, the beam of electrons could not reach the MOS transistor Q. Likewise, secondary electrons or photons generated from the MOS transistor Q could not reach the surface of the device. In Figs. 3A and 3B, which illustrate a first embodiment of the present invention, an aperture 6a is formed in the conductive layer 6. In this case, the aperture 6a opposes the MOS transistor Q, and the shape of the aperture 6a is arranged in parallel with the gate electrode 2. Therefore, even when damage occurs in the gate insulating film (not shown) or the PN junction between the semiconductor substrate 1 and the impurity diffusion regions 3 and 3', such damage can be easily detected by using the above-mentioned evaluation/analysis apparatuses. In Figs. 4A and 4B, which illustrate a second embodiment of the present invention, two conductive layers 7 and 7' are added to the elements of Figs. 3A and 3B. That is, the conductive layers 7 and 7' are made of aluminium and are manufactured simultaneously with the conductive layers 4 and 4'. The conductive layers 4, 4', 7 and 7' are formed on an insulating layer 20-1 which is formed on the semiconductor substrate 1. On the other hand, the conductive layer 6 having the aperture 6a is formed on an insulating layer 20-2 which is formed on the conductive layers 4, 4', 7 and 7'. The conductive layers 7 and 7' are connected to the conductive layer 6 through via-holes 8 formed in the insulating layer 20-2. Therefore, the conductive layers 7 and 7' suppress the increase in resistance of the conductive layer 6 due to the presence of the hollow 6a, thus stabilizing the operation of the device. In Figs. 5A and 5B, which illustrate a third embodiment of the present invention, two N + -type impurity diffusion regions 9 and 9' are added to the elements of Figs. 3A and 3B. That is, the impurity diffusion regions 9 and 9' are manufactured simultaneously with the impurity diffusion regions 3 and 3'. The impurity diffusion regions 9 and 9' are also connected to the conductive layer 6 through via-holes 10 to suppress the increase in resistance of the conductive layer 6 due to the presence of the hollow 6a, thus stabilizing the operation of the device. As explained hereinbefore, according to the present invention, since an aperture is provided in the conductive layer over an element such as a MOS transistor, evaluation/analysis can be carried out without contact by the above-mentioned evaluation/analysis apparatuses.

Claims: A semiconductor device comprising: a semiconductor substrate (1) ; at least one circuit element formed in said semiconductor substrate (1) and having electrodes (2, 4, 4') on said semiconductor substrate (1) ; an insulating layer (20, 20-1, 20-2) formed on said semiconductor substrate (1) so as to cover said circuit element and said electrodes; and an elongated power supply conductor strip (6) formed on said insulating layer (20, 20-1, 20-2) and having a predetermined width and extending over said circuit element characterized in that an aperture (6a) is formed in said conductor strip (6) such that said circuit element is not covered by said conductor strip (6) and is accessible for electron beam analysis through said insulating layer (20). A device as claimed in claim 1, characterized by comprising two additional conductor strips (7, 7') formed on said semiconductor substrate (1) on either side of said circuit element and separated from said semiconductor substrate (1) by an insulating layer (20-1) and each connected so as to be in parallel with said conductive strip (6) across said aperture (6a) so as to compensate for the increase of resistance of said conductor strip (6) caused by said aperture (6a). A device as claimed in claim 1, characterized by two conductive impurity regions (9, 9') formed in said semiconductor substrate (1) on either side of said circuit element and each connected so as to be in parallel with said conductive strip (6) across said aperture (6a) so as to compensate for the increase of resistance of said conductive strip (6a) by said aperture.

Inventors: WATANABE MASAYUKI, WATANABE, MASAYUKI, Watanabe, Masayuki, c/o NEC Microcom. System, Ltd.
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1993
Main classification: H01L23
IPC codes: H01L21, H01L23, G01R31