Chip with Light Protection Layer

Abstract

In the case of a chip (1) having an integrated circuit (2), a dielectric mirror coating (3) having at least two dielectric layers (6, 7, . . . H, I, H) is applied as light protection means for the at least one integrated circuit (2) on at least one portion of the surface of the chip (1).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows schematically a chip according to the invention, namely in plan view onto the side of the chip on which an integrated circuit is realized.

FIG. 2 shows schematically a further chip according to the invention, namely in plan view onto the side of the chip opposite the side on which an integrated circuit is realized.

FIG. 3 shows in a schematic cross-sectional view a further chip according to the invention.

FIG. 4 shows in a schematic cross-sectional view a dielectric mirror coating and the reflection behavior thereof.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a chip 1 according to the invention, which has an integrated circuit 2. In principle, several integrated circuits can also be realized independently of each other on the chip 1. The integrated circuit 2 is realized on a first side 4 of the chip 1, generally known as the “active side”, and is protected against the effects of light by a dielectric mirror coating 3 applied on the surface of the chip 1.

A relatively large number of dielectric mirror coatings have been known to those skilled in the art for a relatively long period of time from the literature. All dielectric mirror coatings have in common the fact they are composed of two or more dielectric λ/4 layers, immediately successive dielectric layers having a different refractive index. Relating to dielectric mirror coatings, the reader is referred by way of example to Matt Young, “Optik, Laser, Wellenleiter”; Springer, 1997; pp 160-161. Despite this fact, experts in the field of integrated circuit chips have never proposed the use of such dielectric mirror coatings in the case of chips having integrated circuits.

“Light” in the present context is understood to be not only light visible to humans, that is, a wavelength range from 380 nm to 780 nm, but also light from spectral ranges of the infrared and ultraviolet adjoining this range.

According to the embodiment shown in FIG. 1, the dielectric mirror coating 3 is applied on the first side 4 of the chip 1 directly onto the integrated circuit 2. This has the advantage that the dielectric mirror coating 3 also takes on the function of a passivation layer against mechanical and chemical influences on the integrated circuit 2, whereby the manufacture of the chip 1 is also simplified. It is important here that when the integrated circuit 2 is directly exposed to effects of light, as is the case when the chip 1 is mounted on a chip carrier with the first side 4 facing away from the chip carrier, at least the active elements of the integrated circuit 2, such as, for example, transistors, diodes and the like, are protected by means of the dielectric mirror coating 3. Above all, when the chip 1 is constructed as a “Quad Flat Package”, the integrated circuit 2 can be exposed to direct incidence of light.

FIG. 2 shows a chip 1; with this chip 1 the dielectric mirror coating 3 is applied on the second side 5 of the chip 1 opposite the first side 4 and generally called the “passive side”. This embodiment of the invention is above all of advantage when the chip 1 is provided for mounting on a chip carrier with the first side 4 facing towards the chip carrier, as is the case with a construction of the chip 1 as what is known as a flip chip.

The embodiments according to the invention just mentioned ensure that the dielectric mirror coating 3 is always arranged between the light incident upon the surface of the chip 1 and the integrated circuit 2.

The embodiments of the invention illustrated in FIGS. 1 and 2 can be realized both separately and jointly. Thus, both an application of the dielectric mirror coating 3 to the first side 4 and to the second side 5 of the chip 1 and an application of the dielectric mirror coating 3 to just one of the two sides 4 and 5 is possible.

FIG. 3 shows the basic construction of a chip 1 according to the invention with the dielectric mirror coating 3. The chip 1 has a substrate 8, which comprises a semiconductor crystal, for example, doped silicon. The integrated circuit is realized in an active zone 9 of the substrate 8. A passivation layer 10, which protects the chip 1 from chemical influences and moisture, is applied over the integrated circuit, that is, over the active zone 9.

The dielectric mirror coating 3 is applied directly on the passivation layer 10. In the absence of such a passivation layer, the mirror coating 3 is applied directly on the active zone 9, that is, on parts of the active zone 9 of the chip 1 that are to be protected against incidence of light, the chip 1 having already been completed as far as circuit engineering is concerned. As already mentioned above, it is also possible for the dielectric mirror coating 3 to be applied additionally or exclusively on the second side 5 of the chip 1, depending on the preferred use and construction of the chip 1. It should be noted at this point that the ratio to one another of thicknesses of the individual layers 8, 9, 10, H, L, H, . . . 7, 6 illustrated in FIG. 3 is not to scale. The illustration serves merely to demonstrate a basic sequence of the individual layers 8, 9, 10, H, L, H, . . . 7, 6 of the chip 1. Thus, in particular the illustrated thickness ratio between the thickness of the active zone 9, the thickness of which normally lies in the nm—range, and the thickness of the layers 10, H, L, H, . . . 7, 6 lying above it, which thicknesses normally each range in the μm—range, does not correspond to the actual circumstances.

To produce the dielectric mirror coating 3 on the chip 1, virtually completely transparent dielectrics (e.g. SiO₂ and TiO₂) can be used in the wavelength range under consideration. When using dielectrics in the manufacture of the dielectric mirror coating 3 it is of advantage above all that these materials are compatible with the chip production process and are hence integrable without problems in the production process.

A dielectric shall be understood here to mean a substance that conducts no or hardly any current, that is, has a high resistivity (>10¹⁰ Ω). Dielectrics have a large energy band gap of in part more than 10 eV, giving a very low interaction with electromagnetic radiation over a broad spectral range. Depending on specification, dielectric thin-film materials for the manufacture of the dielectric mirror coating 3 are chosen in accordance with their optical, mechanical and chemical suitability.

To produce the dielectric mirror coating 3, layers H, L, H, . . . 7, 6 of dielectrics are applied alternately to the surface or to parts of the surface of the chip 1. Each layer H, L, H, . . . 7, 6 in this case comprises a dielectric, layers having a high and a low refractive index following one after another alternately. Preferably, the dielectric mirror coating 3 comprises layers of two different dielectrics. It is also possible, however, instead of a layer system of two dielectrics to provide a layer system of a plurality of different dielectrics in the case of a chip 1.

In FIGS. 3 and 4, the reference letter H denotes a dielectric layer having a high refractive index, this layer H being, for example, a layer of TiO₂ having a refractive index of 2.40. The reference letter L denotes a dielectric layer having a comparatively low refractive index, this layer L being, for example, a layer of SiO₂ having a refractive index of 1.46. Each of these dielectric layers H, L has, as is customary in dielectric mirror coatings, an optical thickness d of λ/4 (more accurately: d=λ/4n where n=refractive index of the layer). Since a phase change occurs at every second interface, the reflecting waves are superimposed constructively. With a plurality of dielectric layers H, L a reflection degree of more than 99.9% can therefore be achieved for a pre-determinable spectral range. The optimum number of these H, L—pairs for achieving the maximum possible reflectivity is dependent on the absorption and distribution of the layers H, L themselves. The sequence of the layers H having a high refractive index and the layers L having in comparison a lower refractive index can vary from the sequence illustrated in FIGS. 3 and 4 in dependence on the given requirements. Thus, the positions of the layers H, L can be interchanged, so that the layer sequence L-H-L-H-L . . . replaces the illustrated layer sequence H-L-H-L-H.

The dielectric mirror coating 3 can be realized even with two (2) to three (3) dielectric layers H, L, which can also be produced relatively inexactly. With a mirror coating 3 of this kind comprising two (2) to three (3) layers H, L it is already possible to achieve a reflectivity of 80% or more.

If the outermost dielectric layer 6 of the mirror coating 3 adjoins air or a medium having a low refractive index, then it is advantageous for this outermost dielectric layer 6 to have a higher refractive index than the inner dielectric layer 7 following immediately thereafter, since in this case a large proportion of the incident light is already reflected at the outermost dielectric layer 6.

The quality of the interfaces of the individual layers H, L of the dielectric mirror coating 3 is also important. By different coating techniques, it is possible to influence the properties of the individual layers and the constitution of the interfaces as determining factors for the overall layer system of the dielectric mirror coating 3. The preferred techniques for applying the dielectric layers to the surface of the chip 1 are here resistance deposition, electron beam vapor deposition, laser-assisted electron beam vapor deposition, ion beam-assisted vapor deposition and plasma ion-assisted vapor deposition. Moreover, the coating process can additionally be optimized by pre-heating of the chip 1.

With just relatively few dielectric layers H, L—even with two (2) to three (3) layers—a pre-determined degree of reflection for a pre-determinable wavelength range can be achieved with the dielectric mirror coating 3.

The mode of operation of the dielectric mirror coating 3 is illustrated in FIG. 4. Some of the incident light is reflected at each interface between two dielectric layers H, L. The reflection at each higher-refracting H results in a phase jump through 180°. The radiation reflected at the interfaces from high-refracting to low-refracting material does not have this phase jump. In combination with the optical thicknesses of the layers of λ/4, these circumstances ensure that the phase shift of the radiation superpositioning at the surface corresponds exactly to an uneven multiple of 180°. The superpositioning of the partial beams reflected at the interfaces is therefore constructive.

Primarily, the reflectance of the dielectric mirror coating 3 as far as its resonance wavelength is concerned depends only on the number of H, L—pairs, the ratio of the refractive indices of high-refracting and low-refracting materials and to a minor extent also on the refractive index of the substrate 8.

The reflectance of the dielectric mirror coating 3 is wavelength-dependent, the reflection in a region around the central wavelength being very high and reducing at larger and smaller wavelengths. The breadth of the highly-reflected spectral range largely depends on the refractive index ratios of the layer materials used. The higher are the refractive index ratios of the dielectric layer materials, the greater also is the spectral bandwidth of the dielectric mirror coating 3.

To summarize, the merit of the invention lies in rendering possible the realization of an effective light-protection means for chips, even for very thin chips, in a cost-effective and simple manner through the use of a dielectric mirror coating known per se in various forms in the field of chips having at least one integrated circuit.

Claims

1. A chip having at least one integrated circuit and having light protection means for the at least one integrated circuit, wherein a dielectric mirror coating having at least two dielectric layers is applied as light protection means on at least a portion of the surface of the chip.

2. A chip as claimed in claim 1, wherein the dielectric mirror coating is applied on at least a side of the chip on which the at least one integrated circuit is realized, at least over a region of the at least one integrated circuit, in which region active elements of the at least one integrated circuit are realized.

3. A chip as claimed in claim 1, wherein the dielectric mirror coating is applied at least on a side of the chip that lies opposite the side on which the at least one integrated circuit is realized.

4. A chip as claimed in claim 1, wherein the outermost dielectric layer of the dielectric mirror coating has a higher refractive index than an immediately proximate, inner dielectric layer.

5. A method for the manufacture of a chip having at least one integrated circuit and having light protection means for the at least one integrated circuit, wherein a dielectric mirror coating is applied as light protection means on at least a portion of the surface of the chip and wherein at least one dielectric layer having a high refractive index and a dielectric layer having a low refractive index are applied to the chip to provide the dielectric mirror coating.

6. A method as claimed in claim 5, wherein the dielectric mirror coating is applied on at least a side of the chip on which the at least one integrated circuit has already been realized, at least over a region of the at least one integrated circuit, in which region active elements of the at least one integrated circuit are realized.

7. A method as claimed in claim 5, wherein the dielectric mirror coating is applied on a side of the chip that lies opposite the side on which the at least one integrated circuit has already been realized.

8. A method as claimed in claim 5, wherein a layer having a higher refractive index than an immediately proximate, inner dielectric layer is applied as outermost dielectric layer of the dielectric mirror coating.