Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Smart card package
Reexamination Certificate
2000-12-06
2004-07-06
Lee, Eddie (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Smart card package
C257S729000, C257S795000
Reexamination Certificate
active
06759736
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a semiconductor device having a substrate on a first side of which there are provided a first semiconductor element and at least one security coating which comprises a powdery filler incorporated in a matrix.
The invention also relates to a smartcard provided with a semiconductor device comprising a memory and a security coating which comprises a powdery first filler incorporated in a matrix.
U.S. Pat. No. 5,399,441 discloses a semiconductor device of the type mentioned in the opening paragraph wherein the security coating is a layer having a matrix of silicon oxide in which a powdery filler is incorporated. When the matrix is filled with a filler, such as an oxide, a nitride or a carbide of silicon, aluminum or a metal, the coating inhibits at least 90% of the transmission of visible light. When the matrix is filled with an inorganic salt of a heavy metal, the coating inhibits at least 90% of the transmission of a specific type of infrared radiation.
It is a drawback of the known semiconductor device that about 10% of the radiation of selected wavelengths is still transmitted through the coating. Considering that state-of-the art microscopes operate with visible light or near infrared radiation, this percentage is too high to provide adequate security. Personal or financial data contained in the known semiconductor device will be accessible and a method to change the data illegally might be found by reverse engineering of the semiconductor device. So if the known semiconductor device is applied in a smartcard and if the smart card falls into the hands of a dishonest person, the data therein will be vulnerable to a breach of security.
SUMMARY OF THE INVENTION
It is, therefore, a first object of the invention to provide a semiconductor device of the type mentioned in the opening paragraph wherein the coating inhibits transmission of visible light and of near infrared radiation to a larger extent. It is a second object to provide a smart card of the type mentioned in the opening paragraph whose semiconductor device has such an improved coating.
The first object is achieved in that:
the difference between the refractive index of the powdery first filler and that of the matrix is at least 0.3, and
the coating comprises a second filler which is a substantial absorber of radiation of wavelengths at least in the range of from 800 to 1400 nm and is free of heavy metals.
The second filler is a material, for example, in the form of particles which transforms incident radiation into heat. As a substantial absorber of radiation, it absorbs the radiation for at least 99 percent. The second filler absorbs the radiation to at least 1400 nm. Radiation of a wavelength larger than 1.4 &mgr;m need not be absorbed as much as 99%, as the large wavelength itself hides details of the first semiconductor element in the semiconductor device of the invention. Preferably, the second filler absorbs the radiation of wavelengths in the range of from 800 to 2000 nm. Suitable materials are, for instance, titanium nitride and titanium oxynitride.
The second filler in a preferred embodiment comprises titanium nitride. Due to the use of titanium nitride as a second filler, of the transmittance of at least 99.9% of radiation of a wavelength of between 600 and 2000 nm can be easily inhibited. The inventors have found that particles of TiN in the coating can have a surface comprising TiO
2
, which is believed to follow from accidental oxidation. Such oxidation occurs, for example, when the security coating is applied during the manufacture of the semiconductor device from an acid, aqueous composition.
A first advantage of this second filler is that titanium nitride is known to be used in the manufacture of semiconductor devices in cleanroom facilities. Moreover, it is free of heavy metals. This is an important advantage as heavy metals are poisonous materials that present problems both during the production and as waste after disposal of the semiconductor device comprising the security coating. A further advantage is that titanium nitride is commercially available in various particle sizes.
The first filler present in the security coating of the device of the invention operates by scattering visible light. Radiation in the visible spectrum as well as in the ultraviolet spectrum is thus inhibited from penetrating by scattered reflection. In order to ensure that the coating has sufficient scattering potential, it was found that the difference between the refractive index of the first filler and that of the matrix should at least be 0.3. As the refractive index of a matrix is generally of the order of 1.4-1.5, first fillers with a refractive index larger than 1.7-1.8 can be used. Examples of such first fillers include oxides of zirconium, titanium, zinc, manganese, chromium, niobium, iron, nickel, strontium, yttrium, vanadium, gallium, copper and cobalt and nitrides of niobium, titanium and zirconium.
The first filler in a further embodiment comprises titanium oxide. This material has a very high refractive index and causes, therefore, intense scattering of visible light and of radiation in the ultraviolet spectrum. If titanium nitride is used as the second filler, it is preferred to have a weight ratio of titanium oxide and titanium nitride in the range of from 0.25 to 4 in the coating.
The amount of filler used in the coating of the semiconductor device of the present invention can be varied over a wide range, depending, for example, on the electrical characteristics desired in the coating. Generally speaking, the first and the second filler are present in a combined amount in the range of from 10 to 90 percent by weight of the coating. The first and the second filler are preferably present as particles of a size in the submicron range.
The material of the matrix of the coating can be chosen from several materials, such as a mono(metal)phosphate compound wherein the metal is, for example, chosen from the group of zinc and aluminum, or a component prepared from a silica precursor resin. Such matrices are described, for example, in the non-prepublished application WO IB99/01007 and in U.S. Pat. No. 5,399,441. Preferably, monoaluminum phosphate is used for the matrix. As a result of the use of this material, the security coating has a great mechanical strength and a good etching persistency. Furthermore, the coating with monoaluminum phosphate can be readily provided in a thickness ranging from 1 to 10 &mgr;m.
In a preferred embodiment the coating has a thickness in the range of from 1 to 5 &mgr;m. It is especially preferred to have a coating thickness of less than 3 &mgr;m. The coating is nevertheless opaque to visible light and near infrared radiation. A first advantage is that the thickness of the semiconductor device is only slightly increased by the provision of the security coating. This is advantageous for the use of the semiconductor device of the invention in a smartcard in which the device thickness is limited. A second advantage is that it is also possible to apply more than one coating in the semiconductor device. A third advantage is that the application of end-contacts in the manufacture of the semiconductor device is easier than in the case of coatings of larger thickness. These end-contacts can be applied by way of a method successively comprising the steps of depositing a photoresist in regions where end-contacts are desired; depositing and drying a composition comprising fillers incorporated in a matrix; removing the photoresist and the composition deposited thereon; heating so as to form the security coating; and applying an electrically suitably conducting material, such as copper, in said regions. Using a coating thickness of less than 5 &mgr;m facilitates the removal of the photoresist and the coating deposited thereon.
If desired, other materials may also be present in the coating. For instance, an agent which modifies the surface of the fillers for better adhesion or a dispersion agent may be used.
A further embodiment of the semiconductor d
Bohmer Marcel René
Kooyman Nicolaas
Koninklijke Philips Electronics , N.V.
Lee Eddie
Owens Douglas W
Zawilski Peter
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