Semiconductor device and its producing method

TECHNICAL FIELD

0001The present invention generally relates to semiconductor devices and more particularly to a pad electrode structure for use in semiconductor devices.

0002In semiconductor devices, it is necessary to form protrusion electrodes on pad electrodes for external connection, such that the pad electrodes, formed inside a semiconductor device on a semiconductor substrate, are connected to a substrate (such as interposer) used for mounting the semiconductor device thereon, electrically and also mechanically.

BACKGROUND ART

0003Generally, at the time of manufacture of semiconductor devices, it is necessary to ensure that each of the semiconductor devices shows electrically normal operation, upon completion of the manufacturing steps of the semiconductor device. For this purpose, it is practiced to carry out electric operational test by contacting a probe needle upon the pad electrodes formed on the semiconductor substrate.

0004In such operational test, it is necessary to press the probe needle against the pad electrode of Al or Cu, and thus, there is formed a flaw (hereinafter probe mark) on the surface of the pad electrode by the sharply pointed probe needle in such a manner that the surface of the pad electrode undergoes an irregular deformation.

0005<figref idref="f0001">Figure 1</figref> is a diagram of the semiconductor device for the case a bump is formed on the pad electrode carrying such a probe mark.

0006Referring to <figref idref="f0001">Figure 1</figref>, a pad electrode 20 is formed on a semiconductor substrate 10 and a passivation film 30 is formed such that the pad electrode 20 is exposed. Further, a probe mark 40 is formed on the surface of the pad electrode 20 as a result of the operational test.

0007On such a pad electrode 20, a Ti layer 60 and a Cu layer 61 are formed by a sputtering method respectively as an adhesion layer and a conductive layer, with respective thicknesses of 300nm and 250nm. Further, a Ni layer 80 and an Au layer 90 are formed respectively with the thicknesses of 4000nm and 200nm, by conducting an electrolytic plating process while using the conductive layer 61 as an electrode. It should be noted that the Au layer 90 functions as an oxidation prevention film of the Ni layer 80.

0008Further, a bump electrode 100 is formed on the Au layer 90 by a lead-free solder such as the solder of the Sn-Ag system or a lead solder such as the solder of the An-Pb system.

0009In the example of <figref idref="f0001">Figure 1</figref>, it should be noted that there is formed a probe mark 40 on the pad electrode 20 as a result of the operational test as explained before, and because of this, there can be a case in which no uniform formation of the adhesion layer 60 or the Cu layer 61 is made by the sputtering process, because of existence of the irregularity forming the probe mark 40. Because the Ti layer 60 or the Cu layer 61 is very thin, having the thickness of only 200 - 300nm, it is not possible to achieve uniform film formation in the case there exists projections and depressions in the underlying layer as in this case.

0010Thus, in the case a Ni layer 80 and an Au layer 90 are formed by an electrolytic plating process while using the Cu layer 61 as an electrode, there occurs no growth of these layers on the probe mark 40, and thus, there can be a case, in the event a bump 100 is formed on the foregoing Au layer 90, that a void 110 is formed between the pad electrode 20 and the bump 100 in correspondence to the probe mark 40.

0011When there exists such a void 110 underneath the bump electrode 100, there occurs degradation of electrical or mechanical properties in the junction that uses such a bump electrode, and the reliability of the semiconductor device is degraded. Further, there can occur a problem that the metal element such as An, Ag, Pb, Ni, and the like, forming the material of the bump electrode, cause diffusion into the pad electrode 20, or Al forming the pad electrode 20 cause diffusion into the bump electrode 100, via the region where no such a Ti layer or Cu layer is formed. Thereby, increase of contact resistance is invited.

0012US patent published under <patcit id="pcit0001" dnum="US6251694B1"><text>US 6,251,694B1 to Liu</text></patcit> et al discloses an example of a semiconductor chip wherein a testing area of the chip is distinct from the connecting area. The publication mentions that if the connecting area is used for testing purposes as well, a peeling of the metal in that area may occur.

0013Thus, in the prior art, it was not possible to achieve a contact of the probe electrode directly on the electrode pad surface, and it has been practiced to carry out the electric operational test by providing a separate electrode pad on the semiconductor device for probe test. In such an approach, however, there occurs an increase in the area of the semiconductor device in view of the need of providing such separate pad electrode for the probe test, in addition to the pad electrodes on which the bump electrodes are formed.

DISCLOSURE OF THE INVENTION

0014Accordingly, it is the concrete object of the present invention to provide a novel and useful manufacturing process of a semiconductor device wherein the foregoing problems are eliminated.

0015A more specific object of the present invention is to provide a semiconductor device allowing direct formation of a bump electrode on a pad electrode to which a probe needle has been contacted.

0016A semiconductor device and a method of manufacturing the semiconductor device according to the invention are defined in the independent claims.

0017According to the present invention, a conductive layer can be formed on said electrode pad including the part where the probe flaw is formed, by forming a protective film on the pad electrode where an irregular flaw (hereinafter a probe flaw) is formed by a probe needle used at the time of the probe testing. Thus, by forming a conductive pattern by conducting an electrolytic plating process while using such a conductive layer as an electrode, it becomes possible to form a bump electrode on the pad electrode. Thereby, the present invention eliminates the need of providing a separate pad electrode for testing, and the surface area of the semiconductor device is used efficiently. Further, the semiconductor device can be miniaturized.

0018Other features and advantages of the present invention will become apparent from the following detailed description about preferred embodiments made with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

0019<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Figure 1</figref> is a diagram showing a semiconductor device for the case a bump is formed on a pad electrode carrying a probe flaw;</li><li><figref idref="f0001">Figure 2</figref> is a diagram showing the process of bump formation on a pad electrode according to a first embodiment of the present invention;</li><li><figref idref="f0002">Figure 3</figref> is another diagram showing the process of bump formation on a pad electrode according to the first embodiment of the present invention;</li><li><figref idref="f0002">Figure 4</figref> is another diagram showing the process of bump formation on the pad electrode according to the first embodiment of the present invention;</li><li><figref idref="f0003">Figure 5</figref> is another diagram showing the process of bump formation on the pad electrode according to the first embodiment of the present invention;</li><li><figref idref="f0003">Figure 6</figref> is another diagram showing the process of bump formation on the pad electrode according to the first embodiment of the present invention;</li><li><figref idref="f0004">Figure 7</figref> is another diagram showing the process of bump formation on the pad electrode according to the first embodiment of the present invention;</li><li><figref idref="f0004">Figure 8</figref> is another diagram showing the process of bump formation on the pad electrode according to the first embodiment of the present invention;</li><li><figref idref="f0005">Figure 9</figref> is another diagram showing the process of bump formation on the pad electrode according to the first embodiment of the present invention;</li><li><figref idref="f0005">Figure 10</figref> is another diagram showing the process of bump formation on the pad electrode according to the first embodiment the present invention;</li><li><figref idref="f0006">Figure 11</figref> is a diagram showing the process of bump formation on the pad electrode according to an example which does not form part of the present invention;</li><li><figref idref="f0006">Figure 12</figref> is another diagram showing the process of bump formation on the pad electrode according to the example of <figref idref="f0006">Figure 11</figref>.</li><li><figref idref="f0007">Figure 13</figref> is another diagram showing the process of bump formation on the pad electrode according to the example of <figref idref="f0006">Figure 11</figref>;</li><li><figref idref="f0007">Figure 14</figref> is another diagram showing the process of bump formation on the pad electrode according to the example of <figref idref="f0006">Figure 11</figref>;</li><li><figref idref="f0008">Figure 15</figref> is a diagram showing the process of bump formation on the pad electrode according to another example which does not form part of the present invention;</li><li><figref idref="f0008">Figure 16</figref> is another diagram showing the process of bump formation on the pad electrode according to the example of <figref idref="f0008">Figure 15</figref>;</li></ul>

BEST MODE FOR IMPLEMENTING THE INVENTION

[FIRST EMBODIMENT]

0020<figref idref="f0001 f0002 f0003 f0004 f0005">Figures 2 - 10</figref> show the process of manufacturing a semiconductor device according to a fist embodiment of the present invention.

A. FORMATION STEP OF PAD ELECTRODE AND SUBSTRATE PROTECTION FILM

0021Referring to <figref idref="f0001">Figure 2</figref>, an aluminum film is formed on the peripheral part of a semiconductor substrate 210 formed with transistors and multilayer interconnections (not shown) by an electron beam evaporation deposition process or a sputtering process, and a pad electrode 220 is formed as a result of pattering of the same. Next, a silicon nitride film 230 is formed on the pad electrode 220 as a protective film so as to cover the pad electrode 220, and an opening is formed in the protective film 230 so that the pad electrode 220 is exposed.

B. PROBE TEST STEP OF THE SEMICONDUCTOR DEVICE

0022After forming the structure shown in <figref idref="f0001">Figure 2</figref>, the step of <figref idref="f0002">Figure 3</figref> is conducted and a probe test is carried out for confirmation of electric signals.

0023As a result, as shown in <figref idref="f0002">Figure 3</figref>, there is formed a probe flaw 240 (referred to hereinafter as probe flaw) on the pad electrode 220 after the probe test in the form of a flaw of uneven shape as a result of urging of the probe needle thereto.

C. SILICON NITRIDE FILM FORMATION STEP ON THE PROBE FLAW ON THE PAT ELECTRODE SURFACE

0024Further, in the step of <figref idref="f0002">Figure 4</figref>, a film such as a silicon nitride film is formed on the structure of <figref idref="f0002">Figure 3</figref> so as to cover the probe flaw 240, and a silicon nitride film pattern 250 is formed in correspondence to the probe flaw 240 as a result of patterning of the silicon nitride film such that the silicon nitride film pattern 250 covers the probe flaw 240.

D. FORMATION STEP OF Ti LAYER AND Cu LAYER

0025Next, in the step of <figref idref="f0003">Figure 5</figref>, a Ti layer 260 and a Cu layer 261 are formed consecutively on the structure of <figref idref="f0002">Figure 4</figref> so as to cover the pad electrode 220 and the silicon nitride pattern 250 by a sputtering process, with respective thicknesses of 300nm and 200nm.

E. PATTERNING STEP OF RESIST FILM

0026Next, in the step of <figref idref="f0003">Figure 6</figref>, a resist film 270 is formed on the structure of <figref idref="f0003">Figure 5</figref>, and patterning of the resist film is made such that the resist film covers the region other than the pad electrode.

F. FORMATION STEP OF Ni LAYER AND Au LAYER

0027Next, in the step of <figref idref="f0004">Figure 7</figref>, a Ni layer 280 is formed on the structure of <figref idref="f0003">Figure 6</figref> by an electrolytic plating process with the thickness of 4000nm, followed by formation of an Au layer 290 on the Ni layer 280 as an oxidation prevention layer with the thickness of 200nm.

G. REMOVAL PROCESS OF RESIST FILM

0028Next, in the step of <figref idref="f0004">Figure 8</figref>, ashing process is conducted and the resist film 270 of <figref idref="f0004">Figure 7</figref> is removed.

H. ETCHING STEP OF Ti LAYER AND Cu LAYER

0029Next, in the step of <figref idref="f0005">Figure 9</figref>, the Ti layer 260 and the Cu layer 261 are removed except for the region of the pad electrode 220 by etching or ion milling while using the Ni layer 280 and the Au layer 290 formed on the pad electrode 220 as a mask.

I. FORMATION STEP OF BUMP

0030Further, in the step of <figref idref="f0005">Figure 10</figref>, a leas-free solder of a Sn-Ag alloy or a lead solder of Sn-Pb alloy is formed on the Au layer 290 in the step of <figref idref="f0005">Figure 10</figref> by any of a printing method, transfer method or electrolytic plating method. Further, by conducting an annealing processing to the solder, a bump electrode 300 is formed.

0031In the present embodiment, on the other hand, it becomes possible to form the Ti layer 260 and the Cu layer 261 on the pad electrode 220 so as to cover the silicon nitride film pattern 250 continuously, by forming a protective film such as the silicon nitride film 250, which is an inorganic film, such that the protective film covers the probe flaw 240 on the surface of the pad electrode 220. Thereby, it is possible to form a Ni pattern 280 or an Au pattern 290 continuously on the pad electrode 220 by an electroplating process so as to cover the region corresponding to the pad electrode 220 uniformly. As a result of this, there occurs no void formation contrary to the conventional case, even when a bump electrode 300 is formed thereon. Such formation of the silicon nitride film 250 between the adhesion layer and the pad electrode 220 is extremely useful in the case the pad electrode 220 carries a flaw such as probe flaw.

0032It should be noted that, while description has been made in the present embodiment for the case the protective film pattern 250 is formed of an insulation film such as a silicon nitride film, the present invention is by no means limited to such a construction and it is also possible to use other insulation film such as a silicon oxide film or an organic film such as a polyimide film, or alternatively a conductive film of a metal or alloy, for the protective film pattern 250. For example, it is possible to obtain a similar effect by forming a conductive film of any of Ag, Pt, Pd and Cu in the form of paste, in place of the protective film pattern 250.

[EXAMPLE]

0033<figref idref="f0006 f0007">Figures 11 - 14</figref> are diagrams showing the fabrication process of a semiconductor device according to an example which does not form part of the present invention, wherein those parts corresponding to the parts described previously are designated by the same reference numerals and the description thereof will be omitted.

A. PROBE TEST STEP OF SEMICONDUCTOR DEVICE

0034As shown in <figref idref="f0006">Figure 11</figref>, there is formed an irregular flaw on the surface of the pad electrode 220 as the probe flaw 240 on the semiconductor substrate 210, as a result of the probe test process conducted after formation of the pad electrode 220 and the substrate protection film 230.

B. PLANARIZATION STEP OF PROBE FLAW BY DRY ETCHING

0035Next, as shown in <figref idref="f0006">Figure 12</figref>, a dry etching process is conducted at the surface of the pad electrode 220 so as to include the probe flaw 240, an the probe flaw 240 is planarized.

C. FORMATION STEP OF Ti LAYER AND Cu LAYER

0036Next, in the step of <figref idref="f0007">Figure 13</figref>, the Ti layer 260 and the Cu layer 61 are formed on the structure of <figref idref="f0006">Figure 12</figref> consecutively by a sputtering process so as to cover the substrate protective film 230 and the pad electrode with respective thicknesses of 300nm and 200nm.

D. FORMATION STEP OF BUMP

0037Thereafter, the steps of Embodiment 1 explained wit reference to <figref idref="f0003 f0004 f0005">Figures 6 - 9</figref> is conducted, and the Ni layer 280 is formed on the Cu layer 261 on the pad electrode 220 with the thickness of 4000nm and the Au layer 290 with the thickness of 200nm. Further, a lead-free solder alloy of Sn-Ag system or a lead solder alloy of Sn-Pb system is formed, and the bump electrode 300 is formed by conducting an annealing process.

0038In this way, the present example enables continuous and uniform formation of the Ti layer 260 and the Cu layer 261 on the pad electrode 220 continuously by planarizing the irregularity step of the probe flaw 240, and it becomes possible to form the bump electrode 300 without forming void.

0039In the present example, the planarization of the probe flaw 240 has been conducted by dry etching. On the other hand, it is also possible to obtain a similar result by using a wet etching process in place of the dry etching process. Further, it is also possible to planarize the probe flaw 240 by fusing the pad electrode 220 at the temperature of 600 - 800°C. Further, it is possible to obtain a similar effect by applying a mechanical pressure to the probe flaw 240 in place of the dry etching process and thus conducting the planarization of the probe flaw 240 mechanically.

[EXAMPLE]

0040<figref idref="f0008">Figures 15 - 16</figref> are diagrams showing the manufacturing process of the semiconductor device according to an example which does not form part of the present invention, wherein those parts in the drawing corresponding to those parts described previously are designated by the same reference numerals and the description thereof will be omitted.

0041Referring to <figref idref="f0008">Figure 15</figref>, the present example forms, after the probe test step, the Ti layer 262 and the Cu layer 263 by a sputtering process so as to cover the pad electrode 220 carrying thereon the probe flaw 240 and the passivation film 230, consecutively with a larger thickness of 500nm, for example.

0042Thereafter, by conducting the process of <figref idref="f0003 f0004 f0005">Figures 6 - 9</figref> explained previously, the Ni layer 280 is formed on the Cu layer 263 on the pad electrode 220 with the thickness of 4000nm and the Au layer with the thickness of 200nm by an electrolytic plating process as shown in <figref idref="f0008">Figure 16</figref>. Further, a lead-free solder alloy of the Sn-Ag system or the Pb alloy of the Sn-Pb system is formed. Further, by applying an annealing process to the solder alloy, the bump electrode 300 is formed.

0043In the present example, the step height of the probe flaw 240 is relatively reduced or becomes ignorable, by forming the Ti layer 262 and the Cu layer 263 with a large thickness preferably equal to or larger than the step height of the probe flaw 240, such as the thickness of about 1µm. With this, it becomes possible to form the Ti layer 262 and the Cu layer 263 continuously on the pad electrode 220.

0044In the foregoing embodiment, it should be noted that the adhesion layer 260 is not limited to a Ti layer but may be formed of any of Ti, Cr, TiW, Mo, Ta, W, Nb and V. Further, it should be noted that the electrode layer 261 is not limited to Cu but can be formed of any of Ni, Cu, Pd, Pt, Au and Ag. Further, the process of forming these is not limited to a sputtering process but evaporation deposition process or MOCVD process can also be used.

0045Further, the conductive layer 280 forming the foundation layer of the bump (UMB layer: under bump metal) is not limited to the Ni layer but may be formed of an alloy containing Ni and Cu. Further, the oxidation prevention layer 290 is not limited to Au but can be formed of any of Au, Pt, Pd and In.

0046Further, the bump electrode 300 is not limited to the Sn-Au alloy or Pb-Sn alloy but an alloy of Pd, Ni, Cu, Sn and Pb, or Au or Ag may also be employed.

0047Further, the present invention is not limited to the preferred embodiment described heretofore, but is subjected to various variations and modifications within the scope of the present invention set forth in patent claims.

INDUSTRIAL APPLICABILITY

0048According to the present invention, it becomes possible to form a conductive film on a pad electrode stably and continuously even when the pad electrode formed on a substrate carried thereon an irregular flaw. Thus, by conducting an electrolytic plating process while using such a conductive film as an electrode, it becomes possible to form a conductive layer on the front surface of the pad electrode. As a result, it becomes possible to form a bump electrode on such a conductive layer stably, without forming a void.

0049According to the present invention, it becomes possible to form a bump electrode also on the pad electrode to which the probe electrode is contacted. Thereby, the need of forming a separate pad electrode for testing is eliminated, and the substrate surface area can be used efficiently. Further, the semiconductor device can be miniaturized.