Optical semiconductor device having photosensitive diodes and process for fabricating such a device

An optical semiconductor device includes, in a zone (5), a structure of photosensitive diodes including a matrix (6) of lower electrodes (7), an intermediate layer (9) made of a photosensitive material formed on the matrix of lower electrodes and at least one upper electrode (10a) formed on the intermediate layer, in which an electrical connection (3a) includes at least one electrical contact pad (7a) and at least one electrical connection pad (16a) are produced beneath the intermediate layer, at least one electrical connection via (14) is produced through the intermediate layer and connects the upper electrode to the electrical contact pad and at least one well (15a) is formed outside the zone (5) and passes through at least the intermediate layer (9) in order to expose the electrical connection pad (16a). Also provided is a process for fabricating such a device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims priority from prior French Patent Application No. 05 00408, filed on Jan. 14, 2005, the entire disclosure of which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of optical semiconductor devices, and more particularly to an optical semiconductor device having a structure of photosensitive diodes.

2. Description of the Related Art

U.S. Pat. No. 6,455,836 discloses a photosensitive semiconductor device that comprises, on top of a base layer, an intermediate layer made of a photosensitive material, projecting lower electrodes in this layer and an upper layer that includes an upper electrode. A lateral well passes through the intermediate layer and the upper layer. The base layer includes connection means that are connected selectively to the lower electrodes and comprise connection pads placed in the bottom of the aforementioned well. A local layer made of an electrically-conductive non-transparent material covers some of the diodes in order to form an optical barrier and extends along the sidewalls and in the bottom of the well so as to electrically connect the upper electrode to the electrical connection pads. Such an arrangement is not suitable for implementation on standard fabrication machines, especially planarization machines, and requires a tricky final operation to produce the local layer.

Accordingly, there exists a need for overcoming the disadvantages of the prior art as discussed above.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides an optical semiconductor device comprising photosensitive diodes of simplified structure and simplified fabrication.

The first subject of the present invention is a semiconductor device comprising, in a zone, a structure of photosensitive diodes comprising a matrix of lower electrodes, an intermediate layer made of a photosensitive material formed on the matrix of lower electrodes, and at least one upper electrode formed on the intermediate layer.

According to the invention, the device comprises, beneath the intermediate layer, electrical connection means that include at least one electrical contact pad and at least one electrical connection pad.

According to the invention, the device comprises at least one electrical connection via passing through at least the intermediate layer and connecting the upper electrode to the electrical contact pad.

According to the invention, the device has at least one well formed outside the zone and passing through at least the intermediate layer, this well exposing the electrical connection pad.

According to the invention, the device preferably comprises a lower dielectric layer in which the matrix of lower electrodes and the at least one electrical contact pad are formed and, beneath this lower layer, a base layer in which the at least one electrical connection pad is formed, the at least one well passing through this lower layer in order to expose this electrical connection pad.

According to the invention, the device preferably includes an upper layer comprising a first layer constituting the second electrode and a second layer made of an electrically conductive material, the at least one via and the at least one well passing through this upper layer.

According to the invention, the device preferably includes a non-transparent local layer that partly covers the structure of photosensitive diodes.

According to the invention, the local layer is preferably made of an electrically conductive material, the at least one via being connected to this local layer.

According to the invention, the device preferably includes at least one transparent outer protective layer.

Another subject of the present invention is a process for fabricating an optical semiconductor device comprising a multiplicity of photosensitive diodes comprising lower electrodes and at least one upper electrode that are separated by an intermediate layer made of a photosensitive material.

According to the invention, this process consists of: producing a base layer that includes electrical connection means; forming a dielectric lower layer above the base layer; forming, in the lower layer, a matrix of lower electrodes that are selectively connected to the electrical connection means; producing an intermediate layer made of a photosensitive material on the lower layer; forming an upper layer made of an electrically conductive transparent material; forming at least one via made of an electrically conductive material through the intermediate and upper layers so as to electrically connect the upper layer and at least one of the lower electrodes; and producing at least one well through the lower, intermediate and upper layers so as to expose at least one electrical connection pad of the electrical connection means, the at least one electrical connection pad being connected to the at least one via.

According to the invention, the at least one via is preferably produced above the corresponding lower electrode.

According to the invention, the process preferably consists in forming an upper layer comprising a first layer made of a first electrically conductive material and a second layer made of a second electrically conductive material.

According to the invention, the process preferably consists in forming a local layer made of a non-transparent material above the upper layer and extending partly above the multiplicity of photosensitive diodes.

According to the invention, the process preferably consists in forming a protective outer layer made of a transparent material.

DETAILED DESCRIPTION

Referring toFIGS. 1 and 2, these show a semiconductor device1in the final state.

This device1comprises a dielectric base layer2that includes electrical connection means3flush with its surface and, on this base layer, a dielectric lower layer4.

This lower layer4includes, in a zone5, a matrix6of lower electrodes7that are flush with its surface and are selectively connected to the electrical connection means3by electrical connections vias8. The lower electrodes7may in particular be made of chromium or n-doped silicon.

The device1includes, on the lower layer4, an intermediate layer9made of a photosensitive material which may in particular be amorphous or polycrystalline silicon.

The device1includes, on the intermediate layer9, a transparent upper layer10formed by a first layer10aof a first electrically conductive material, constituting an upper electrode, and a second layer10bmade of a second electrically conductive material. The first layer10amay in particular be p-doped silicon and the second layer10bmay in particular be ITO (indium tin oxide).

The device1includes, on the intermediate layer10, an insulating transparent outer protective layer11.

The device1includes, on the outer layer11, a non-transparent local layer12that, in the example, extends in the form of a ring covering the lower electrodes of two or three outer rows of the matrix6. This local layer12may in particular be made of a metal of the Al or Ti/TiN type.

The device1has holes13that extend through the aforementioned layers9,10and11, between the local layer12and the lower electrodes7aof the outer row of the matrix6of lower electrodes. These holes are filled with an electrically conductive material, for example copper, constituting vias14for electrically connecting the layer10by lateral contact to the lower electrodes7athat constitute electrical connection pads. The local layer12extends or passes over the vias14and so is connected to these vias and to the branch3athrough these vias.

Advantageously, the local layer12and the vias14can be made with the same material. They can be realized in a single step of the process.

It follows from the foregoing that, with the exception of the peripheral zone corresponding to the vias14associated with the lower electrodes7a, the device1has a structure6aof photosensitive diodes formed between the remaining lower electrodes7band the upper electrode10a. The photosensitive diodes located facing the central aperture in the local annular layer12are sensitive to the external light, while the photosensitive diodes located beneath this non-transparent local annular layer12are not sensitive thereto.

Outside the zone5, and therefore outside the local annular layer12, the device1has a multiplicity of wells15distributed around its periphery, which pass through the layers4,9,10and11. These wells expose electrical connection pads16that are selectively connected to the electrical connection means3.

In particular, a well15aexposes an electrical connection pad16athat is exclusively connected to the electrodes7a, and therefore to the upper electrode10, by the intermediary of the vias14and of a branch3a.

The device1can be connected to any other electrical or electronic means by the intermediary of electrical connection wires17, the ends of which are respectively introduced into the wells15and bonded to the corresponding electrical connection pads.

One method of fabricating the semiconductor device1described above, employing known techniques, especially etching, deposition and planarization, will now be described with reference toFIGS. 3 to 8.

AsFIGS. 3 and 4show, after the connection means3have been produced in the base layer2and its surface has been planarized, the process continues with the deposition of the upper layer4. The vias8are produced, and then the matrix6of lower electrodes7.

AsFIG. 5shows, after the surface of the layer4, including the vias8and the lower electrodes7, have been planarized, the process continues with the deposition of the intermediate layer, of the layer10, by successively depositing its first layer10aand its second layer10b, and of the outer layer11, optionally with intermediate planarization operations being carried out.

AsFIG. 6shows, holes13are produced through the layers9,10and11, down to just above the peripheral lower electrodes7a.

AsFIG. 7shows, the vias14are then produced, followed by the local layer12.

Finally, the wells15are produced through the layers4,9,10and11down to the connection pads16so as to finally obtain the device as shown inFIGS. 1 and 2.

As shown inFIGS. 2 and 4, preferably several devices1located beside one another are produced on a common base layer2, by carrying out the aforementioned operations jointly. Each individual device1is then produced, for example by sawing.

Referring toFIG. 8, it may be seen that, according to an alternative embodiment, it would optionally be possible to deposit an additional transparent outer protective layer11aon the front of the outer layer10and of the local layer12.

Referring toFIG. 9, this shows that, according to another alternative embodiment, it would be possible to form the vias14through the layers9and10, to form the local layer12on the upper layer10and then optionally to form the outer protective layer11on the front of this upper layer10and of this local layer12.

The present invention is not limited to the examples described above.

In particular, the local layer12does not go right around the matrix6but, for example, it could be limited to one side of this matrix. The number of vias14could be reduced, and these vias could be provided only around part of the periphery of the matrix6. Many other alternative embodiments are possible without departing from the framework defined by the appended claims.

While there has been illustrated and described what is presently considered to be embodiments of the present invention, it will be understood by those of ordinary skill in the art that various other modifications may be made, and equivalents may be substituted, without departing from the true scope of the present invention.

Additionally, many modifications may be made to adapt a particular situation to the teachings of the present invention without departing from the central inventive concept described herein. Furthermore, an embodiment of the present invention may not include all of the features described above. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the invention include all embodiments falling within the scope of the appended claims.