Semiconductor device with read out prevention and method of producing same

A semiconductor device has antenna pads and a testing pad formed on the substrate. An insulating resin layer containing a filler covers the testing pad, and bumps are provided on the antenna pads. Specific data in the semiconductor device are inhibited from being read out or rewritten, by the provision of the insulating resin layer containing a filler.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method of producing the semiconductor device. In particular, the present invention relates to an electrode structure of a semiconductor device formed as a nonvolatile memory, and to a structure for preventing an operation of intentionally reading out the internal data and a method for its production.

2. Description of the Related Art

In recent years, IC cards and, particularly, IC tags mounting a semiconductor device formed as a nonvolatile memory have been widely produced and used. In such semiconductor devices, part of the internal data is written as specific data in such a manner that data cannot be written and read out, and data are suitably written into a writable memory portion.

A nonvolatile memory IC for an IC tag includes antenna pads and a testing pad.FIG. 10illustrates a conventional nonvolatile memory IC for an IC tag. The IC includes antenna pads2and a testing pad3, formed on a substrate1, and Au stud bumps4are formed on the antenna pads2. The testing pad3is exposed for testing (for writing data). Reference numeral5denotes an inorganic insulating film and6denotes an organic insulating film.

In the above IC, a test is conducted after the antenna pads2and the testing pad3are formed, by bringing a testing probe into contact with the antenna pads2and with the testing pads3. A needle scar7is formed on the antenna pads2and the testing pads3at portions where the probe comes into contact.

In the IC tags, the internal specific data, in most cases, must be kept secret and may be a history of the products and personal data. If the internal specific data can be read out or can be rewritten, it is possible that the data can be incorrectly used, which is not desirable.

For example, Japanese Unexamined Patent Publication (Kokai) No. 2003-142539 (pp. 4-6, FIG. 3) discloses a semiconductor device and a method of testing a semiconductor device. According to this testing method, a probe is brought onto a desired terminal without problem even if the surface of the substrate is rough to some extent. As illustrated inFIG. 10, therefore, the data can be read out by bringing the probe into contact with the testing pad3even when there is a protrusion such as a stud bump4on the surface of the substrate and a difference in height between the stud bump4and the testing pad3. Therefore, the internal specific data may be incorrectly used.

Further, the Au stud bump4is expensive to fabricate, and it is desired to fabricate the bumps at a low cost. It is therefore desired to employ a method, of forming the bumps, relying upon electrolytic plating or non-electrolytic plating.

Also, in the fabrication process, the bump is formed on the antenna pad after the steps in which the data are written and the probe is brought in contact with the testing pad. When the bump is formed by electrolytic plating, a seed layer for UBM plating (UBM; under bump metal or under barrier metal) is formed and, then, a metal is plated thereon to form a bump on the antenna pad. If the seed layer (UBM; under bump metal or under barrier metal) is formed on the pads2and3where the needle scars7of the probe remain in a protruded manner, then, the protruded portions of the pads are not covered with the underlying layer to a sufficient degree. Namely, the plated bump metal and the pad metal come into direct contact with each other, a diffusion reaction takes place during use, and the bump strength becomes drops.

Also, in the method of forming bumps relying on the non-electrolytic Ni plating, hydrogen, which is produced during the non-electrolytic Ni plating, penetrates a passivation film and enters into the ferroelectric layer and it becomes probable that the pinning phenomenon occurs to make it difficult to rewrite the data.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductor device which inhibits specific data, inside the device, from being read out and inhibits the data from being written again and a method of producing the semiconductor device.

A semiconductor device, according to the present invention, comprises a substrate, antenna pads formed on the substrate, a testing pad formed on the substrate, an insulating resin layer containing a filler covering the testing pad, and bumps provided on the antenna pads.

In this constitution, the testing pad, other than the antenna pads, is covered with the insulating resin containing the filler. Therefore, even if an unauthorized person attempts to bring the probe into contact with the testing pad, the probe is not easily brought into contact with the testing pad through the insulating resin containing the filler. Besides, even if it is attempted to remove the insulating resin by etching, the presence of the filler makes etching impossible.

A method of producing a semiconductor device, according to the present invention, comprises the steps of forming antenna pads and a testing pad on a substrate, covering a part of the substrate except for the antenna pads with an insulating resin layer containing a filler, forming a seed layer for plating on the antenna pads and the insulating resin layer containing the filler, and plating the seed layer for plating to form bumps on the antenna pads.

In this constitution, the probe is not allowed to be easily brought into contact with the testing pad through the insulating resin containing the filler. Besides, with the surface of the testing pad being smoothed prior to covering the testing pad other than the antenna pads with the insulating resin layer containing the filler, the scar made by the probe becomes smooth in the step of testing. Further, the protrusion of the testing pad becomes smooth in forming the bump by the electrolytic plating in a subsequent step. Therefore, the testing pad is well covered with the UBM layer, and the bump is formed reliably.

A method of producing a semiconductor device, according to the present invention, comprises the steps of forming antenna pads and a testing pad on a substrate, covering a part of the substrate except for the antenna pads and the testing pad with an insulating resin layer containing a filler, forming a seed layer for plating on the antenna pads, the testing pad and the insulating resin layer containing a filler, plating the seed layer for plating to form bumps on the antenna pads, and removing the seed layer for plating and the testing pad except for the antenna pads.

Further, a method of producing a semiconductor device, according to the present invention, comprises the steps of forming antenna pads and a testing pad on a substrate, covering a part of the substrate except for the antenna pads with an insulating resin layer containing a filler, forming bumps on the antenna pads by non-electrolytic plating, and covering the surface of the bumps with a solder layer.

In this constitution, a predetermined testing step is effected. Then, after the bumps are formed, the testing pad is removed except for the antenna pads. With the testing pad being removed, the probe can no longer be brought into contact with the testing pad, and the data in the semiconductor device cannot be read out. In this case too, the testing pad is pretreated prior to the step of forming the bumps so that the needle scar is smoothed and, then, the bumps are formed by electrolytic plating.

A semiconductor device, according to the present invention, comprises a substrate, antenna pads formed on the substrate, a testing pad formed on the substrate, and bumps provided on the antenna pads, the bump being mainly made of copper formed by non-electrolytic plating.

In the non-electrolytic plating using copper, hydrogen hardly evolves. Therefore, as hydrogen does not penetrate the passivation film and enter the ferroelectric layer, the pinning phenomenon does not take place. This makes it possible to form a highly reliable semiconductor device at a low cost.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a view illustrating a semiconductor device according to a first embodiment of the present invention, andFIGS. 2A and 2Bare views illustrating a state where a probe is brought into contact with the semiconductor device ofFIG. 1. The semiconductor device10is formed as a nonvolatile memory IC for an IC tag. The semiconductor device10includes antenna pads12and a testing pad13, formed on a substrate (semiconductor wafer, semiconductor chip, etc.)11, and bumps14are formed on the antenna pads12. A semiconductor circuit is formed on the substrate11by a semiconductor process, and the antenna pads12and the testing pad13are connected to the semiconductor circuit.

InFIGS. 1 to 2B, reference numeral15denotes an inorganic insulating film, and16denotes an insulating resin layer containing a filler. Reference numeral17denotes a needle scar and18denotes a seed layer for electrolytic plating (UBM: under bump metal or under barrier metal).

The inorganic insulating film15has openings for exposing the antenna pads12and the testing pad13. The insulating resin layer16containing the filler has openings for exposing the antenna pads12but covers the testing pad13.

Referring toFIG. 2A, after the antenna pads12, the testing pad13and the inorganic insulating film15are formed, and before the insulating resin layer16containing the filler and the pumps14are formed, a test is effected or data are written, by bringing a testing probe19into contact with the antenna pads12and the testing pad13. Needle scars17are formed on the antenna pads12and the testing pad13at portions where the probe19contacts. The needle scar17assumes a form that is partly protruded. After the test using the probe19, the insulating resin layer16containing the filler and the bumps14are formed.

FIG. 2Bis a view illustrating a state where the probe19is brought into contact with the semiconductor device after the insulating resin layer16containing the filler and the bump14are formed. In this case, an attempt is made to bring the probe19into contact with the testing pad13to have access to the data. However, as the testing pad13is covered with the insulating resin layer16containing the filler, the probe19cannot contact the testing pad13and access to the data is not possible.

In the IC tags or the like, the internal specific data are, in most cases, those which need high degree of secrecy, such as a history of the products and personal data. According to the present invention, the internal specific data cannot be read out or rewritten, and there is no possibility that the data are incorrectly used.

It is possible to prevent the probe19from coming into contact with the testing pad13if the testing pad13is covered with a resin layer without filler. When the resin layer without filler has a very small thickness, however, it is possible that the probe19will come into contact with the testing pad13by penetrating the resin layer without filler, despite the testing pad13being covered with the resin layer without filler. If the testing pad13is covered with the insulating resin layer16containing the filler, it is possible to surely prevent the probe19from coming into contact with the testing pad13by penetrating the insulating resin layer16containing the filler. Namely, even if the thickness of the insulating resin layer16containing the filler is very small, the filler works to increase the hardness of the insulating resin layer16containing the filler and prevents the probe19from penetrating the insulating resin layer16containing the filler. Further, even if it is attempted to remove the insulating resin layer16containing the filler by ashing or the like measure, it is difficult to remove the filler which remains.

Silica or acrylic resin can be used as the filler in the insulating resin layer16. Silica or acrylic resin permits light to pass through and can, hence, be used even for the photosensitive resins. When the resin film is formed by printing or the like method, the filler may be metal or one that does not permit light to pass through. For example, a filler comprising silica particles having the size of 1 to 2 μm is mixed in an amount of 30 to 40% by weight into the resin. The insulating resin layer16containing the filler has a thickness of, for example, 3 to 6 μm.

It is desired that the resin used for the insulating resin layer16containing the filler is one that can be cured at, for example, not higher than 230° C. to prevent the data in the nonvolatile memory from being disturbed by heat. Examples of the resin material include silicone resin and epoxy resin. The insulating resin layer16containing the filler has a sufficient thickness to cover the needle scar17. The substrate (semiconductor chip)11, on the other hand, has a small thickness. Therefore, if the insulating resin layer16containing the filler has a large thickness, warping occurs. It is, therefore, desired that the insulating resin layer16containing the filler has a thickness which is as small as possible.

FIGS. 3A to 3Fare views illustrating a method of producing the semiconductor device ofFIG. 1.FIG. 3Aillustrates a state where the substrate11is subjected to semiconductor processing to form the antenna pads12and the testing pad13and the test is carried out. A needle scar17may be formed. The inorganic insulating film15has openings to expose the antenna pads12and the testing pad13.

FIG. 3Billustrates a state where a pretreatment is effected to smooth the surface of the testing pad13prior to covering the testing pad13except for the antenna pads12with the insulating resin layer16containing the filler. As a result, the needle scar17becomes small. The pretreatment is effected by etching such that the height of the needle scar17becomes smaller than 2.5 μm. Due to the treatment, the shape of the needle scar17is smoothed.

FIG. 3Cillustrates a state where a part of the substrate11including the testing pad13and except for the antenna pads12is covered with the insulating resin layer16containing the filler. The insulating resin layer16containing the filler is selected, for example, from a photosensitive insulating resin and is formed to have a thickness of not smaller than about 4 μm. Silica or acrylic resin is used as the filler.

FIG. 3Dis a view showing a state where an underlying layer18for electrolytic plating is formed on the surface of the substrate11having the insulating resin layer16containing the filler formed thereon by using a sputtering apparatus. The seed layer18is formed by using, for example, Ti.FIG. 3Eis a view showing a state where a resist20of a predetermined pattern is formed on the underlying layer18.FIG. 3Fis a view showing a state where the bumps14are formed on the underlying layer18at portions thereof exposed through the openings in the resist20by effecting the electrolytic plating using the resist20as a mask. The bumps14comprise, for example, Au plating.

After the step ofFIG. 3F, the resist20is removed, the underlying layer18is etched, and formation of the bumps is finished. This state is illustrated inFIG. 1.

FIG. 4is a view illustrating a semiconductor device according to a second embodiment of the present invention. The semiconductor device10of this embodiment resembles the semiconductor device10ofFIG. 1. In this embodiment, however, the testing pad13ofFIG. 1is removed, and a cavity13A is formed at a portion where the testing pad13has been provided. Further, an insulating resin layer16A containing a filler is provided instead of the insulating resin layer16containing a filler. The insulating resin layer16A containing the filler exposes the cavity13A where the testing pad13has been provided.

FIG. 5is a view illustrating a state where the probe19is brought into contact with the semiconductor device ofFIG. 4. In this case, it is attempted to bring the probe19into contact with the testing pad13to access the data. However, as there is no testing pad13, the probe19cannot be brought into contact with the testing pad13, and the data are not accessible.

FIGS. 6A to 6Fare views illustrating a method of producing the semiconductor device ofFIG. 4.FIG. 6Aillustrates a state where the substrate11is subjected to a semiconductor process to form the antenna pads12and the testing pad13and the test is carried out. There is formed a needle scar17. The inorganic insulating film15has openings to expose the antenna pads12and the testing pad13.

FIG. 6Billustrates a state where a pretreatment is effected to smooth the surface of the testing pad13. As a result, the needle scar17is reduced.FIG. 6Cis a view illustrating the formation of the insulating resin layer16A containing the filler. The insulating resin layer16A containing the filler has openings for exposing the antenna pads12and the testing pad13. It is possible to arrange that the insulating resin layer16A does not contain a filler.

FIG. 6Dis a view illustrating a state where the underlying layer18for electroplating is formed on the surface of the substrate11having the insulating resin layer16A containing the filler formed thereon by using a sputtering apparatus. Further, a resist20of a predetermined pattern is formed on the underlying layer18, the electroplating is effected using the resist20as a mask, and the bumps14are formed on the underlying layer18at portions thereof exposed through the openings in the resist20. The bumps14are formed by using, for example, Au plating.FIG. 6Eis a view illustrating a state where the resist20is removed, the underlying layer18is etched, and formation of the bumps is finished.

FIG. 6Fis a view illustrating a state where the etching is further effected to remove the testing pad13. Therefore, the insulating resin layer16A containing the filler exposes the cavity13A at a place where the testing pad13was provided. The testing pad13is made of Al. In this case, the testing pad13is removed while controlling the etching rate by using a phosphoric acid-type etchant, so that the inner layer wiring remains in the substrate11.

FIG. 7is a view illustrating the semiconductor device according to a third embodiment of the present invention. The semiconductor device10of this embodiment resembles the semiconductor device10ofFIG. 1. In this embodiment, however, the bumps14are mainly made of copper formed by non-electrolytic plating, which is covered with a solder layer21.

FIGS. 8A to 8Fare views illustrating a method of producing the semiconductor device ofFIG. 7.FIG. 8Aillustrates a state where the substrate11is subjected to the semiconductor process to form the antenna pads12and the testing pad13and the test is carried out. There is formed a needle scar17. The inorganic insulating film15has openings to expose the antenna pads12and the testing pad13.

FIG. 8Billustrates a state where a pretreatment is effected to smooth the surface of the testing pad13. As a result, the needle scar17dwindles.FIG. 8Cis a view illustrating the formation of the insulating resin layer16A containing a filler. The insulating resin layer16A containing the filler covers the testing pad13.

FIG. 8Dis a view illustrating a state where the resist20of a predetermined pattern is formed on the surface of the substrate11having the insulating resin layer16containing the filler formed thereon and, besides, the bumps14are formed by non-electrolytically plating with copper by using the resist20as a mask.FIG. 8Eis a view illustrating a state where the resist20is removed to finish the formation of bumps.FIG. 8Fis a view illustrating the formation of the solder layer21covering the bump14. In this case, the solder layer21may be formed as required. Further, the bump14may be formed using not only a copper layer but also a plurality of layers including those of other materials (e.g., Ni and Au).

Usually, the formation of the bump by the non-electrolytic plating is carried out by a Ni-plating. However, hydrogen which is produced during the non-electrolytic Ni-plating penetrates the passivation film and enters the ferroelectric layer, giving rise to the occurrence of a pinning phenomenon which makes it difficult to rewrite the data. In this embodiment, therefore, the bump14is formed by electrolytic plating with copper, which produces little hydrogen and eliminates the possibility that the data cannot be rewritten into the nonvolatile memory, at a low cost.

FIGS. 9A to 9Care views illustrating an example of an IC tag including the semiconductor device of the present invention.FIG. 9Ais a plan view illustrating an IC tag22to which the semiconductor device10is connected and secured.FIG. 9Bis a view schematically illustrating a portion of the semiconductor device10together with an antenna circuit23of the IC tags22.FIG. 9Cis a side view illustrating the IC tag22to which the semiconductor device10is connected and secured. The semiconductor device10is connected and secured to the IC tag22through the bumps14. The IC tag22has the antenna circuit23, and the bumps of the semiconductor device10are connected to the antenna circuit23of the IC tag22. InFIG. 9, the testing pad13is not illustrated. The data in the IC tag22are read out without contact by an apparatus body that is not shown.

According to the present invention, as described above, the specific data in the semiconductor device are inhibited from being read out or rewritten. Namely, the semiconductor device can be safely and reliably used as a nonvolatile memory.