Patent Description:
Semiconductor devices are generally manufactured and packaged as individual devices such as diodes or transistors, or as integrated circuits ICs, each integrated circuit chip typically comprising thousands or several million interconnected electrical devices fabricated on a single compact semiconductor substrate or wafer.

The fabrication of semiconductor integrated circuits may involve two processing stages: the front-end-of-line (FEOL) processing stage and the back-end-of-line (BEOL) processing stage. The FEOL covers everything up to, but not including, the deposition of metal interconnect layers. At this stage, the patterning of the individual electronic devices that form part of the integrated circuit directly onto a semiconductor substrate or wafer takes place. A process known as front-end surface engineering also occurs, which comprises the growing of surface oxides to form elements such as gate dielectrics, the patterning of such gate devices and/or any essential electronic elements, for example, channels, source and drain regions, and the implantation or diffusion of dopants to produce the suitable charge carriers in the semiconductor material required to achieve the desired device characteristics.

The BEOL processing stage commences upon completion of the FEOL processing. At this stage, electrical contacts or pads, interconnect wires, vertical electrical connections that pass through a semiconductor wafer (vias) and dielectric structures are formed. Typically, more than ten metal layers can be added to a modern IC during the BEOL process. Also included in this stage is the cutting or singulating of the finished wafer into individual semiconductor die. Each of the separated dies are then packaged for structural support, package interconnect and ingress protection. For example, the separated individual dies may be mounted on a bespoke package substrate having pins or contact pads for interconnection with other system components. Internal to the bespoke package, the contact pads on the semiconductor die are electrically connected to the contact pads within the package to complete the circuit.

A chip scale package (CSP) is an example of an integrated circuit or a discrete package that employs FEOL and BEOL processes during fabrication. In accordance with industry standards, a CSP should have a package area or footprint that is no greater than <NUM> times that of the semiconductor die encapsulated within the package and the CSP must be in the form of a single-die, direct surface-mountable package. CSPs generally have no packaging comprising an insulation material used to encapsulate and protect the semiconductor dies. The back or top portion of the device is exposed for receiving pattern marking for chip identification purposes. A pattern mark may for example include a part number, a date of manufacture, a company logo, a place of manufacture, or any other information.

Small CSPs have a relatively small surface area on the back or top exposed portion, which may make pattern marking for chip identification problematic using existing marking technologies, because there is limited space for such marking. Known pattern marking technologies include, for example, laser ablation, photolithography or photolithography with subsequent etching. In laser ablation, a beam of a laser is focused onto a semiconductor substrate thereby breaking down the chemical bonds within the area to which the beam is applied and selectively removing material on the surface of the substrate. In laser ablation, the laser intensity, pulse length, and wavelength, as well as the semiconductor material itself, influence the amount of surface material to be removed. During microfabrication, photolithography may also be used to transfer a desired pattern marking to a film or semiconductor substrate by applying light through a photomask to a light-sensitive chemical "photoresist" on the semiconductor substrate. Both marking process are limited either by the resolution of the laser for the ablation process or by the resolution of the inspection camera at customer side.

A pattern marking on a CSP smaller than chip package size code <NUM> (i.e. an approximate package dimension of <NUM> × <NUM>) is limited by the resolution of the pattern processes and tools used. Small pattern markings are generally expensive and difficult to create. For example, on a <NUM> product, the back or top portion of the package typically only provides an exposed area sufficient to accommodate a single patterned character using laser ablation. The variability of a single patterned character or single digit is therefore limited to approximately <NUM> letters and <NUM> numbers.

Another issue that may arise relates to the optical recognition of product pattern markings in small CSPs using optical inspection tools. Small features used in such product markings may not be of a suitable resolution that would allow an optical inspection tool to correctly read and identify a CSP product.

<CIT> pertains to a coloured encapsulation layer in which an additive/pigment is added to provide the colour. The colour provides part of a machine readable identifier.

<CIT> pertains to a titanium oxide insulating identification layer in which a region is white and another region has been irradiated with a laser to convert to titanium dioxide, rendering the region black and forming an identification mark. <CIT> pertains to laser engrave an encapsulation to provide an identifier. <CIT> pertains to providing a code pattern provided outside an active area of a wafer, the active area being provided in a separate die area, the code pattern being associated with the die area.

Aspects and embodiments of the invention have been devised with the foregoing in mind.

The invention is as defined in independent claim <NUM> and the dependent claims.

For a more complete understanding of the present disclosure, reference is now made to the following description taken in conjunction with the accompanying drawings in which:.

The claimed subject-matter provides exemplary semiconductor CSP comprising a machine readable identifier in which the identifier comprises a colour marking (i.e. a colour-coded machine readable identifier).

The machine readable identifier may also be applied to other semiconductor devices, such as, for example, bare dies or in general active semiconductor chips.

Conventional pattern marking methods impose limitations on the minimum allowable device marking dimensions, which is typically governed by the laser ablation spot size, the resolution of the optical recognition optics and/or the resolution of pattern markings. The use of colour coded marking, (i.e. by applying colour to the device surface for marking) may negate these limitations by avoiding the need to use pattern marking altogether where the device surface for marking is too small.

According to the present disclosure, colour coded marking may also be used in combination with pattern markings, for example, where the device surface for marking is sufficiently large enough to allow a single pattern marking. This may increase the marking variability to (<NUM> letters and <NUM> numbers) multiplied by applicable colours.

According to the present disclosure, the application of a colour coded marking to a surface portion of a CSP may be achieved by integrated process steps during the fabrication of the CSP or by additional process steps post completion of the fabrication process of a CSP.

In the integrated process steps method, colour coded markings may be applied to CSP packaging during the fabrication process of the device at the final stage where an insulation material layer is applied to the outer surface of the CSP packaging for protective purposes by, for example, Atomic Layer Deposition (ALD). Colour coded markings may also be applied to the CSP by separately introducing colour as a by-product during the wafer separation stage by plasma dicing. During separation by plasma dicing, surface modifications are made to create optical scatter lattices. Thus, surfaces of a die, which would be encapsulated in a transparent insulation layer (to permit observation of the surfaces of the die), may be coloured, with the colour dependent upon the type of optical scatter lattice.

ALD is a thin-film deposition method where a film may be grown on a semiconductor substrate or wafer by exposing its surface to alternate gaseous species or precursors. During the CSP fabrication process, thin films may also be applied to a surface of a CSP to protect and seal the device and/or to achieve desired optical reflection properties. ALD enables a user to apply a protective layer on a surface of a CSP device while at the same time independently tune or adjust optical properties of the surface. Depending on the number of thin film layers and the material being added to the surface of the CSP during the ALD process, different colours may be achieved on the surface of the CSP. A detailed discussion of specific ALD processes is not within the scope of the present disclosure as the skilled person will be aware that ALD processes may allow for deposition of near perfect layers by sequential self-limiting surface reactions.

According to one or more embodiments, falling within the scope of the present invention, an aluminium oxide may be deposited on a surface of a CSP by ALD to form an insulation material layer of a fixed thickness (e.g. <NUM> thick) to produce a CSP having a specific colour coded marking on the outer surface, in this case, the colour brown. According to further embodiments, falling within the scope of the present invention, by varying the thickness of the deposited insulation material layer comprising the aluminium oxide, different insulation material layers with different colour coded markings may be achieved as illustrated in <FIG>. For example, four easily distinguishable coloured thin films: purple, blue, green and orange may be produced with Al<NUM><NUM><NUM> of thicknesses: <NUM>, <NUM>, <NUM> and <NUM> respectively.

An insulation material layer with colour coded marking may also be achieved by mixing aluminium oxide with other materials such as titanium oxide. Al<NUM>O<NUM> alone may be corroded by moisture, therefore the inclusion of the TiO<NUM> layer improves corrosion resistance because TiO<NUM> is chemically more stable than Al<NUM>O<NUM>. According to one or more embodiments, falling within the scope of the present invention, an insulation material layer is formed of one or more bi-layers of aluminium oxide and titanium oxide.

Colour coded marking may be achieved on such an insulation material layer by first applying an aluminium oxide thin film layer on a surface of the CSP and then applying a titanium oxide thin film layer over the first layer to form a bi-layer. Identical bi-layers may then be repeatedly deposited over the first bi-layer to build up an insulating material layer of a desired thickness to achieve an insulation material later with a required colour coded marking. The stacking order of the metal oxides may also vary such that, for example, the first thin film layer applied on the surface of the CSP may be titanium oxide and the second thin film layer may be aluminium oxide. According to the embodiments, any suitable metal oxides alone or in combination can not be used other than aluminium and titanium oxide to achieve insulation material layers with colour coded markings. The deposited layer of oxide material may be of any suitable thickness to achieve a desired colour coded marking. The colour is determined by the sum of thicknesses of all deposited layers, which includes a protection layer.

The typical range of the insulating material layer thickness may be in the range of <NUM> to <NUM> such that a wide spectrum of colour coded markings can be achieved, and the requirement of total package volume is maintained as nearly identical to the volume of the die. For illustrative purposes, <FIG> shows three different colour coded semiconducting wafers produced in accordance with the method set out in the preceding paragraphs. Each wafer comprises approximately <NUM> devices (i.e. <NUM> sized). The colouring of a top surface of these wafers may be achieved by stacking multiple bi-layers of titanium oxide TiO<NUM> and aluminium oxide Al<NUM>O<NUM> using the ALD process. For illustrative purposes, <FIG> shows conceptual views of three finished CSP products (<NUM> sized), each comprising one of the three wafer examples with colour coded markings shown in <FIG>.

To achieve a "purple" colour, an insulating layer comprising Al<NUM>O<NUM> and TiO<NUM> with a thickness of <NUM> may be employed. To achieve a "blue" colour, an insulating layer comprising Al<NUM>O<NUM> and TiO<NUM> with a thickness of <NUM> may be employed. To achieve a "yellow" colour, an insulating layer comprising Al<NUM>O<NUM> and TiO<NUM> with a thickness of <NUM> may be employed.

In the integrated process step method, additional to the ALD process, colour coded marking may also be applied to the CSP as a by-product during plasma dicing. Plasma dicing is a process used for cutting or singulating wafers, i.e. separation of wafers during fabrication.

There are two methods using plasma dicing for separation, called "grinding before dicing" (GBD) and "dicing before grinding" (DBG). Both methods are also adoptable to blade dicing, which is more common, A common process for Plasma dicing is called "Bosch process". This dry etching process creates a scalloped sidewall on a die, which may work as an optical grid by the formed grooves parallel to one of the two major surfaces called back side or front side. In dependency of the size of the grooves and the incident angle of the incident light, the surface appears coloured.

Plasma dicing employs a dry etching process that makes use of fluorine chemistry. Unlike blade dicing, where contact is made between a blade and the wafer during cutting which may lead to the wafer chipping or cracking, no physical contact is made with plasma dicing. In addition, unlike blade dicing which require more blade processing time to perform more cut lines, the dicing process time for plasma dicing remains more or less the same regardless of the chip size. Plasma is therefore suited for cutting micro-sized chips of <NUM> square or smaller.

A by-product of plasma dicing is the formation of multi-coloured strips on the semiconductor wafer surface during the singulating process. That is, walls of the CSP may appear multi coloured, because of some slight process variation and grooves/stripes.

In the additional process steps method, colour coded marking may be applied to the CSP device after completion of the fabrication of the CSP device or semiconductor wafer. During the final fabrication process step of the CSP, an insulation material layer is applied to the outer packaging of the CSP device to encapsulate and protect the semiconductor die within the device. When this process is completed, separate or additional fabrication process steps may be performed to apply colour coded marking on top of the insulation material. The colour coded marking may be a type of paint, a dye, etc..

<FIG> illustrates a semiconductor CSP <NUM> falling within the scope of the present invention, and comprising a semiconductor die <NUM> and a plurality of electrical contacts <NUM>. The die <NUM> is encapsulated in an insulating layer <NUM>, which is Al<NUM>O<NUM>, or a combination of Al<NUM>O<NUM> and TiO<NUM>.

A colour of the insulating layer <NUM> is dependent upon the thickness of the Al<NUM>O<NUM> layers, or the sum of the thicknesses of Al<NUM>O<NUM> and TiO<NUM> layers (where both materials are present).

<FIG> illustrates a semiconductor CSP <NUM> falling within the scope of the present invention only when the insulating layer is a layer of aluminium oxide or a stack of one or more bi-layers of aluminium oxide and titanium dioxide. Otherwise <FIG> is an example not forming part of the present invention but useful for understanding it. The semiconductor CSP <NUM> comprises a semiconductor die <NUM> and a plurality of electrical contacts <NUM>. The die <NUM> is encapsulated in an insulating layer <NUM>, which comprises an additive. The additive comprises a colouring additive that provides a colour component to the insulating layer <NUM>.

<FIG> illustrates a semiconductor CSP <NUM> falling within the scope of the present invention only when the insulating layer is a layer of aluminium oxide or a stack of one or more bi-layers of aluminium oxide and titanium dioxide. Otherwise <FIG> is an example not forming part of the present invention but useful for understanding it. The semiconductor CSP <NUM> comprises a semiconductor die <NUM> and a plurality of electrical contacts <NUM>. The die <NUM> is encapsulated in an insulating layer <NUM>, an outer surface of which is coated with a layer <NUM> containing an additive. The additive comprises a colouring additive that provides a colour component to the insulating layer <NUM>.

<FIG> illustrates a semiconductor CSP <NUM> falling under the scope of the present invention only when the insulating layer is a layer of aluminium oxide or a stack of one or more bi-layers of aluminium oxide and titanium dioxide. Otherwise <FIG> is an example not forming part of the present invention but useful for understanding it. The semiconductor CSP <NUM> comprises a semiconductor die <NUM> and a plurality of electrical contacts <NUM>. The die <NUM> is encapsulated in a layer <NUM> containing an additive. The additive comprises a colouring additive that provides a colour component to the layer <NUM>. A transparent insulating layer <NUM> surrounds the layer <NUM> and allows the underlying layer <NUM> to be observed.

<FIG> illustrates a semiconductor CSP <NUM> falling under the scope of the present invention only when the insulating layer is a layer of aluminium oxide or a stack of one or more bi-layers of aluminium oxide and titanium dioxide. Otherwise <FIG> is an example not forming part of the present invention but useful for understanding it. The semiconductor CSP <NUM> comprises a semiconductor die <NUM> and a plurality of electrical contacts <NUM>. The die <NUM> is encapsulated in an insulating layer <NUM>, which comprises surface formations <NUM> in an outer surface thereof. These surface formations provide a colour component. Optionally, the surface formations <NUM> comprise optical lattices.

Claim 1:
A semiconductor chip scale package comprising:
a semiconductor die (<NUM>), the semiconductor die comprising: a first major surface opposing a second major surface; a plurality of side walls extending between the first major surface and second major surface;
a plurality of electrical contacts (<NUM>) arranged on the second major surface of the semiconductor die (<NUM>); and
an insulating layer (<NUM>) disposed on the plurality of side walls and on the first major surface, said insulating layer comprising a machine readable identifier by which a semiconductor chip scale packaging type is identifiable by an identification apparatus that reads said machine readable identifier, wherein said machine readable identifier comprises a colour component,
wherein the insulating layer (<NUM>) is a layer of aluminium oxide or a stack of one or more bi-layers of aluminium oxide and titanium dioxide, said insulating layer (<NUM>) having a predetermined thickness being such that it has a specific colour corresponding to said colour of the machine readable identifier.