Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Bump leads
Reexamination Certificate
2002-03-15
2004-05-11
Flynn, Nathan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Bump leads
C257S777000, C257S750000, C257S676000, C257S787000
Reexamination Certificate
active
06734556
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a so-called chip-on-chip (hereinafter abbreviated as COC) type semiconductor device, in which a plurality of semiconductor chips is electrically interconnected as opposed to each other, and a method for manufacturing the same. More particularly, the invention relates to a semiconductor device having such a construction that two mutually opposed semiconductor chips thereof can be joined to each other without being damaged due to a high temperature applied thereon or mechanical shock by supersonic waves when they are connected to each other and a method for manufacturing the same.
BACKGROUND ART
Conventionally, there has in some cases been used a so-called a COC (chip on chip) type semiconductor device having a construction of composing a semiconductor circuit of a plurality of chips by interconnecting them one on the other for a purpose of, for example, reducing an occupied area by means of three-dimensioning or standardizing part of the circuit (for example, changing driver circuits based on application by standardizing the memory portions), if the semiconductor device is composed of a plurality of circuits like in the case of a combination of memory portions and the corresponding driver circuits.
As shown, for example, in
FIG. 17
showing a process of joining two semiconductor chips
1
and
2
, a semiconductor device having the above-mentioned construction is fabricated by fixing the one semiconductor chip
1
on a heated board stage
51
and the other semiconductor chip
2
to a mount head
52
, pressing the mount head
52
to permit bump electrodes
11
and
21
made of Au etc. of the respective chips to come in contact with each other under pressure, and heating it to a temperature of 450° C. or so to interconnect these bump electrodes
11
and
21
electrically. Note here that, as mentioned above, the bumps
11
and
21
are made of a metal material such as Au having a higher melting point than solder because the semiconductor device is mounted on the mother board by soldering.
Since the above-mentioned COC type semiconductor device employs high melting point metal such as Au as the material of its bump electrodes, to interconnect a plurality of semiconductor chips thereof, it is necessary to heat them to a temperature of 450° C. or so under pressure in order to obtain good electrical interconnection. When the chips are heated to such a high temperature during interconnection, the semiconductor substrate is also heated to a temperature of 450° C. or higher, so that the circuit elements formed in the semiconductor substrate (elements such as transistors constituting the semiconductor device) are heated to a high temperature, thus fluctuating in properties, which is a problem. Further, although these chips can be joined to each other at a temperature of 450° C. or so, if under pressure as mentioned above, for example, once joined to each other, they cannot be separated without being destroyed in most cases because Au has a high melting point.
In view of the above, it is an object of the present invention to provide such a COC type semiconductor device and a method for manufacturing the same that has a construction which is capable of interconnecting the electrodes of semiconductor chips without being affected by a temperature at which the semiconductor device is mounted and also without deteriorating the properties of the semiconductor chips owing to a high temperature applied thereon.
It is another object of the present invention to provide a semiconductor device having a construction which is capable of securely connecting a bump electrode of a semiconductor chip, even if small, to a partner semiconductor chip.
It is a further object of the present invention to provide a semiconductor device having a construction which is capable of securely connecting each other in the event that one is a wiring.
It is a still further object of the present invention to provide a semiconductor device having a construction which is capable of securely interconnecting a parent chip and a child chip and separating from each other easily without affecting elements in the semiconductor chips when the child chip is removed.
It is an additional object of the present invention to provide a semiconductor chip having such a construction that avoids force from being concentrated on the bump electrode at a joining portion so that the element formed in a semiconductor layer underlying the joining portion may not be affected adversely.
It is another additional object of the present invention to provide a semiconductor manufacturing method which is capable of joining the bump electrodes at a relatively lower temperature and also easily without accurate alignment thereof.
DISCLOSURE OF THE INVENTION
A semiconductor device according to the present invention includes; a first semiconductor chip having an electrode terminal, a second semiconductor chip having an electrode terminal, a bump electrode made of a first metal for joining the first and second semiconductor chips, the bump electrode being provided on at least one of the electrode terminal of the first semiconductor chip and the electrode terminal of the second semiconductor chip, and an alloy layer formed on a joining portion where the first and second semiconductor chips are joined with each other via the bump electrode, the alloy layer being made of an alloy of the first metal and a second metal, wherein the second metal is made of such a metal that can melt at a temperature lower than a melting point of the first metal and be alloyed with the first metal.
The first or second metal referred to here includes not only pure metal but also an alloy and composite metal made of at least two kinds of metal as well as main metal on the outer layer side in a case of a stack containing at least two kinds of metal. Also, an alloy layer of the first and second metal includes an entirely alloy layer as well as such a layer that part thereof is an alloy and the other part is made of only the first or second metal or any other compound. Further, the constructions of joining via the bump electrode include a construction in which one bump electrode and another are joined to each other or another in which a bump electrode is provided to the electrode terminal of one semiconductor chip so that it may be directly joined to the electrode terminal of the other semiconductor chip therethrough.
By employing such a construction, it is possible to electrically interconnect first and second semiconductor chips by joining their respective electrode terminals at a relatively low temperature by melting the second metal having a relatively low melting point to alloy it with the first metal which the bump electrode is made of. As a result, the bump electrode can be connected at a low heating temperature almost equal to the melting point of the second metal, so that by selecting, for example, Sn as the material of the second metal, it is unnecessary to apply such a heating temperature that may affect the circuit elements, thus avoiding adverse effects on these elements owing to a high temperature. Moreover, the first metal that makes up the major part of the bump electrode has a relatively high melting point and, therefore, causes no trouble at around the soldering temperature during mounting.
According to another aspect of the semiconductor device of the present invention includes; a first semiconductor chip having an electrode terminal, a second semiconductor chip having an electrode terminal, a bump electrode made of a first metal for joining the first and second semiconductor chips, the bump electrode being provided on at least one of the electrode terminal of the first semiconductor chip and the electrode terminal of the second semiconductor chip, and a third metal layer having a lower melting point than that of the first metal provided on a joining portion where the first and second semiconductor chips are joined with each other via the bump electrode. That is, rather than directly forming an alloy with the bump electrode
Flynn Nathan
Greene Pershelle
Rabin & Berdo P.C.
Rohm & Co., Ltd.
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