Active solid-state devices (e.g. – transistors – solid-state diode – With means to prevent inspection of or tampering with an...
Reexamination Certificate
2001-04-16
2003-04-08
Paladini, Albert W. (Department: 2827)
Active solid-state devices (e.g., transistors, solid-state diode
With means to prevent inspection of or tampering with an...
C257S638000, C257S659000, C257S660000
Reexamination Certificate
active
06545371
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor device capable of protecting its circuit arrangement from analysis, thereby making it difficult to imitate or duplicate the circuit or to alter information.
BACKGROUND OF THE INVENTION
A semiconductor device is generally composed of a multiplicity of semiconductor elements provided on a substrate, and wirings provided between electrodes of the semiconductor elements. In such a semiconductor device, to protect the foregoing structure from effects of the external atmosphere, such as &agr; rays, moisture, or stress, a circuit section is protected with a protective film with insularity made of silicon oxide, silicon nitride, or the like. This enables prevention of malfunctions caused by moisture intrusion, etc., changes of characteristics caused by stress, and the like.
Besides, some circuit sections of semiconductor devices are developed as a result of long-time studies, or some are very unique, which are preferably protected so as not to be imitated or copied by others. Moreover, some circuits of semiconductor devices are memory elements in which important information is stored, which are preferably protected so that information therein should not be altered.
The protective films described above are intended to merely protect the circuit section from the external atmosphere, and as to the optical aspect, many of them exhibit good permeability with respect to visible light and far infrared radiation, allowing the circuit section to be easily observed through the protective film by means of visible radiation microscopes or infrared radiation microscopes. This could permit the circuit section to be imitated or copied, and information in memory elements to be altered. Therefore, conventionally, structures as described below have conventionally been adapted to prevent this.
(1) In a structure disclosed in the Japanese Publication for Laid-Open Patent Application No. 165129/1989 (Tokukaihei 1-165129 [Date of Publication: Jun. 29, 1989]), as shown in
FIG. 14
, an integrated circuit includes a circuit section
40
in which a multiplicity of semiconductor elements provided on a semiconductor substrate are mutually connected via wirings, and a protective film
42
with insularity that covers the circuit section
40
. The protective film
42
is made from, for instance, silicon nitride, in which a metallic film
43
with conductivity is provided. Parts of a surface of the circuit section
40
where security protection is not required is covered with only the protective film
42
, while regions of main sections are covered with a lower layer
42
a
of the protective film
42
, a metallic film
43
, and an upper layer
42
b
of the protective film
42
in the stated order.
This ensures that in etching the protective film
42
, an entirety of the protective film
42
is removed from regions where security protection is not required, while only the upper layer
42
b
of the protective film
42
on the metallic film
43
is removed in the regions of the main sections covered with the metallic film
43
. Thus, since the metallic film
43
is not removed, the main sections that require security protection are not exposed, thereby being invisible. Besides, even if the metallic film
43
is removed by etching in the foregoing state, wiring patterns
41
that are made from the same material as that of the metallic film
43
, for instance, aluminum, are also removed, resulting in that the circuit section
40
cannot be analyzed. Thus, by covering the main sections of the circuit section
40
with the metallic film
43
having conductivity while inserting the insulating protective film
42
therebetween, the integrated circuit is protected from being imitated or duplicated by others.
(2) The Japanese Publication for Laid-Open Patent Application No. 154674/1999 (Tokukaihei 11-154674 [Date of Publication: Jun. 8, 1999]) discloses a structure as shown in FIG.
15
. More concretely, on one main surface of a semiconductor substrate
50
wherein an integrated circuit is formed, an insulator isolating layer
51
comprising silicon dioxide (SiO
2
) is deposited. In the insulator isolating layer
51
, first and second wirings
52
and
53
that are made of aluminum (Al) and connected to the integrated circuit, and a shielding layer
54
made of Al are embedded and formed. Opening parts
54
a
and
54
b
are formed in the shielding layer
54
, and connecting layers
55
and
56
made of Al are formed in the same layer as the shielding layers
54
in the opening parts
54
a
and
54
b
. Both ends of the connecting layer
55
are connected to cut-end parts
52
a
of the first wiring
52
through vias
57
made of tungsten (W). Both ends of the connecting layer
56
are connected to cut-end parts
53
a
of the second wiring
53
through vias
58
made of W. A surface-protecting layer
51
b
is formed on the surface of the shielding layer
54
.
In this arrangement wherein the integrated circuit is shielded by the shielding layer
54
and the shielding layer
54
and the connecting layers
55
and
56
are made of the same material and formed in the same layer, an attempt to remove the shielding layer
54
by etching results in removal of the connecting layers
55
and
56
at the same time. Thus, by providing the shielding layer
54
that optically shields the foregoing wirings and by forming the connecting layers
55
and
56
as part of the foregoing wirings in the same layer in that the shielding layer
54
exists, it is possible to prevent the circuit in an operating state from being observed, hence to protect the operating state of the circuit from analysis for the purpose of illegal act.
(3) The Japanese Publication for Laid-Open Patent Application No. 270562/1998 (Tokukaihei 10-270562 [Date of Publication: Oct. 9, 1998]) discloses a structure as shown in FIG.
16
. This structure has a multi-wiring structure in which a polysilicon gate and a wiring
62
are formed on a silicon substrate
61
and a metallic first layer wiring
64
and a metallic second layer wiring
66
are formed on insulating films
63
and
65
, respectively. Incidentally, the metallic second layer wiring
66
is covered with a passivation film
67
. Above the insulating film
65
, an opaque conductive shielding film
60
is formed in the same layer where the metallic second layer wiring
66
is provided, with a gap kept therebetween.
In this structure, the integrated circuit is shielded by the conductive shielding film
60
, and further, removal of the conductive shielding film
60
results in breaking the wirings in the same layer. By providing a system to prevent the inner part of integrated circuit from optically being observed, the reverse engineering of a semiconductor integrated circuit is prevented.
The above-described structures, however, have the following problems.
In the structure of (1), since the upper layer
42
b
made of the same material as that of the lower layer
42
a
is present on the metallic film
43
, stopping the etching of the protective film
42
when the metallic film
43
is exposed makes it possible to etch exclusively the metallic film
43
. This allows to make the lower circuit structure observable, thereby making analysis of the circuit possible.
The structure of (2) is intended to damage the wirings upon removable of the shielding metallic film so as to prevent analysis of the circuit operations. After chemically or physically removing a protective film above the shielding layer
54
and the connecting layers
55
and
56
in the same layer, photolithography may be applied to expose only the shielding layer
54
, whereby removal of only the shielding layer
54
as shielding metallic film is enabled. In the structure of (3) as well, the conductive shielding layer
60
can be removed in an identical manner.
Thus conventionally available are the methods that easily overcome the schemes for preventing a circuit from being copied, duplicated and for preventing recorded information from being altered, and henc
Ban Hiroshi
Matsumoto Hironori
Nakano Akihiko
Ohmi Toshinori
Takeda Tadao
Birch Stewart Kolasch & Birch
Paladini Albert W.
Sharp Kabushiki Kaisha
Thai Luan
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