Patent Application
20080224316
The invention relates to an electronic device and a method for producing electronic devices. The electronic devices can preferably contain an integrated component in a housing body. The integrated component contains for example just one circuit element or a multiplicity of circuit elements, in particular semiconductor circuit elements, e.g. transistors, diodes, sensors, etc. The devices can be produced at the wafer level, the integrated components being singulated if for example a rear side metallization has been produced for all the components of a wafer.
Particular requirements with regard to the electrical or thermoelectric properties are made of power components, for example, which serve for example for switching currents of greater than 1 ampere or greater than 10 amperes. The switching voltages are for example greater than 30 volts or even greater than 300 volts. When producing such power components, wafers, for example, are thinned in order to set the breakdown voltage of vertical semiconductor circuit elements by way of the layer thickness of the wafer. However, in a different context, too, workpieces, in particular semiconductor workpieces, are thinned, for example during the production of SOI substrates (silicon on insulator).
There is a need for a simply constructed device that is simple to produce, in particular a power device. Moreover, there is a need for a simple method for producing a device. In particular, the device is intended to contain a thinned substrate, wherein a reduction of the yield by breakage of the thin workpiece is intended to be avoided in particular during production.
The invention specifies an electronic device, comprising:
Furthermore, the invention specifies a method, comprising the steps of:
Embodiments and, with reference to the figures, exemplary embodiments of the invention are explained below. In the figures:
The following considerations can be taken as a basis in order to use a so-called embedded carrier or so-called mixed material dicing, that is to say the separation of two or more material layers lying one above another transversely with respect to the stacking direction. Adjacent material layers, in particular, have materials which are different from one another, and which therefore have different material properties, in particular mechanical properties such as hardness, brittleness, etc. Wafers, in particular silicon wafers, can be thinned down to a layer thickness of a few micrometres, e.g. to a layer thickness of less than 10 micrometres, or even into the nanometres range, for example down to layer thicknesses of less than 200 nanometres. In this case, a stabilizing carrier which can concomitantly be included in construction can be used, which carrier can be used for example simultaneously as a rear side metal contact. Said carrier can also be referred to as an embedded carrier.
The use of a carrier which can be included in construction can be utilized in particular in mass production, that is to say for example in daily productions of more than 500 wafers. The wafers can be thinned to layer thicknesses of less than 50 micrometres. In this case, a great effort can be required to apply rear side metallizations to such thin wafers. By way of example, a carrier which is separated from the wafer again could be used for this purpose. However, in the course of removing the wafer provided with a rear side metallization from the carrier and subsequent further processing, e.g. testing and inspecting, mechanical damage could then easily occur, such as wafer fracture or edges being knocked off.
A comparably thick rear side metallization can be produced. The metal layer can inherently be used as a carrier. The metal layer can comprise a sequence of different metal layers. The metal layer or the metal layer sequence can typically be thicker than 10 micrometres or thicker than 30 micrometres or even thicker than 50 micrometres. By way of example, the metal layer or the metal layer sequence can have the following tasks:
Consequently, the rear side contact can simultaneously be embodied as a carrier. The rear side contact can be fixedly connected to the chip or integrated component and can be concomitantly included in construction (embedded carrier).
The rear side metal layer functioning as a carrier can be produced by, for example, sputtering, electrodeposition, deposition without external current (possibly with a material seeding layer that is sputtered, applied by vapour deposition or produced by some other method) or by, for example, thermally laminating on a partial layer, as is also customary during the production of printed circuit boards, for example.
During the application of the rear side metal layer, the wafer or some other workpiece slice can be stabilized by a further carrier system, e.g. by a glass plate as in the so-called glass plate method from 3M (Minnesota Mining Manufacturing) . The stable composite composed of active layers, bulk silicon and rear side metal carrier can be released from the further carrier or from the auxiliary carrier and be mounted onto a so-called dicing tape and/or dicing frame for singulation, for example.
The singulation of thin workpiece slices, e.g. wafers, with rear side metal can have various problems. These problems can be solved by two-stage separation:
By way of example, a so-called progressive cutting can be carried out on a cutting machine or on a plurality of cutting machines using different saw blades optimized for silicon and the respective metal. As an alternative, the singulation can be effected by a laser beam, for example. Combinations between sawing and laser separation can furthermore be used.
The electronic device can comprise:
The layer thickness of the first layer region is for example less than 500 micrometres or even less than 300 micrometres in all the aforementioned variants a) to c). To put it another way, as layer thicknesses of the substrate decrease, the first layer region is intended to afford additional stability by additional layer thickness.
The substrate and the first layer region can have identical contours at an interface between the substrate and the first layer region, as is the case for example if a single separating operation is used for singulating the devices. As an alternative, the contours can deviate from one another along the periphery of the interface only by a distance of at most 20 micrometres or of at most 5 micrometres. This is the case for example if two saw blades having different thicknesses are used for singulating the devices in two separating operations. Since the substrate is preferably sawn first, the first layer region can protrude further than the substrate. This is attributable for example to the fact that after the first separating operation using a first saw blade, a further separating operation is carried out using a thinner second saw blade in comparison with the first saw blade.
The device can comprise a housing body, which is arranged at the substrate and at the first layer region. The housing body can contain an epoxy resin or some other polymer material. As an alternative, ceramic housings can also be used. The housing body can serve for protecting the integrated component against environmental influences, such as, for example, moisture, in particular for hermetic protection.
The device can additionally comprise a second layer region arranged at the first layer region. The second layer region can be a part of a so-called leadframe. As an alternative, the second layer region can contain an interposer printed circuit board, a thin-film wiring arrangement or similar wiring arrangements. In all the examples mentioned, the device is then for example also mounted onto a mounting printed circuit board carrying further components arranged in other housing bodies. However, the device can also be mounted directly onto a printed circuit board without a second layer region, for example using flip-chip technology.
The second layer region can be electrically conductive and can comprise in particular a homogeneous material or a layer stack. The layer thickness of the electrically conductive second layer region can be greater than 100 micrometres and preferably less than 800 micrometres. On account of the layer thicknesses mentioned, methods from micromechanics can be used for processing the second layer region.
An electrically conductive connecting layer, for example a solder material layer or a diffusion solder material layer, can be arranged between the first layer region and the second layer region. In this case, the solder materials can have a melting point of less than 400° C. Diffusion solder layers can be produced at temperatures of less than 400° C., but after diffusion soldering have a melting point that is greater than 400° C.
The second layer region can be or comprise a carrier lamina surrounded by connection legs. The carrier lamina and at least one section of each connection leg can preferably be arranged in one plane, as is typical of leadframes. The carrier lamina and the connection legs can be composed of the same material, for example of copper or a copper alloy; preferably, said material can also be provided with a protective layer.
As an alternative, the second layer region can be an interposer printed circuit board, in which thin conductive track layers are enclosed by insulating layers, wherein the thickness of a layer can lie for example within the range of 50 to 150 micrometres. The interposer printed circuit board can preferably be surrounded by the housing body on all sides.
Furthermore as an alterative, the second layer region can be a wiring device produced using thin-film technology. Such wiring devices can have layer thicknesses of less than 20 micrometres even if they contain for example more than one metallization layer. The housing body can preferably be arranged only on one side of the wiring device, as is the case if the thin-film wiring device is arranged directly at the housing body only after the production of the housing body. Thin-film technology, in particular, is very well suited to wafer level production.
The first layer region can contain a first layer which contains copper or comprises copper or a copper alloy having at least 70 atomic percent of copper.
Preferably, the layer thickness of the first layer can be at least 70% of the layer thickness of the first substrate region. Consequently, the first layer is the main layer of the first layer region.
As an alternative, the first layer region can contain a first layer which contains aluminium or comprises aluminium or an aluminium alloy having at least 70 atomic percent of aluminium. Preferably, the layer thickness of the first layer can be at least 70% of the layer thickness of the first layer region, such that the first layer is the main layer of the first layer region.
The abovementioned materials copper and aluminium have a high electrical conductivity and can be processed comparatively simply. In particular, copper can be applied at temperatures of less than 150° C. Aluminium, too, can be applied for example at these temperatures by means of cold sputtering methods. As will be explained in greater detail further below, this can be highly advantageous in the production of the devices.
The device can contain at least one or a multiplicity of high-voltage transistors designed for switching voltages of greater than 30 volts or greater than 300 volts. Examples are DMOS transistors (Double Diffused Metal Oxide Semiconductor) or IGBT elements (Isolated gate Bipolar Transistor). Precisely in the case of these devices, for example the breakdown voltage of a vertical circuit element can be set by means of the thickness of a substrate, wherein the substrate can be thinned during production.
A method is additionally specified, which can comprise the features of:
The releasing process can be effected prior to arranging the first layer in a sawing frame. As an alternative, however, the process of releasing the carrier slice is effected after arranging the first layer in a sawing frame. Preferably, the first layer can be adhesively bonded onto a sawing film, in particular onto a self-adhesive film.
The layer thickness of the first layer is chosen such that the composite composed of workpiece slice and first layer warps by less than 3000 micrometres or by less than 200 micrometres after releasing the layer region. The above-mentioned values hold true particularly in the case of wafers having a diameter of 150 mm, 200 mm or even of 300 mm or more. The reduced warpage makes it possible to use machines and automatic manufacturing systems, in particular wafer transport systems, which are also used for standard wafers, that is to say wafers having the customary layer thicknesses of, for example, 750 micrometres or more.
The method can comprise the feature of:
As an alternative, the method can comprise the feature of:
The carrier slice can comprise a semiconductor substrate or be composed of a semiconductor substrate, in particular a monocrystalline semiconductor substrate or polycrystalline semiconductor substrates such as are used for example in thin film transistor technology (TFT—Thin Film Transistor) or in solar technology. By way of example, silicon, gallium arsenide or other materials can be used as semiconductor materials.
The method can additionally comprise the features of:
The temperature of the workpiece slice can be increased successively in different partial regions when activating the dopants; in particular, a laser beam can be used. This measure prevents relatively great heating of the workpiece. By way of example, the carrier slice is still fitted to the substrate at this point in time. If for example temperatures of 200° C. or even of 140° C. are not exceeded, the carrier slice can be adhesively bonded with the substrate in a simple manner. Low temperatures during production are also advantageous for a metallization as is possibly already present on the front side of the substrate or for integrated components on the front side of the substrate.
Insofar as the word “can” is used in this description, both the possibility and the actual technical realization are meant. Exemplary embodiments are explained below, but, like the abovementioned embodiments as well, they serve only for elucidation and not for restriction.
The electronic device 10 additionally contains a rear side metallization 14, which is fixed to the integrated component 12 for example with the aid of a barrier layer 13. Examples of barrier layers are explained in more detail below with reference to
In the exemplary embodiment, the integrated component 12, the barrier layer 13 and the rear side metallization 14 have the same lateral dimensions in the cross section shown. In other exemplary embodiments, the lateral dimensions in the cross section shown deviate from one another just by a few micrometres, e.g. by less than 10 micrometres. By contrast, the carrier lamina 16 in the exemplary embodiment projects beyond the rear side metallization 14 by a number of micrometres, e.g. by more than 10 micrometres. In other exemplary embodiments, however, the carrier lamina 16a or 16b has a smaller contour than the rear side metallization 14 or, respectively, the same contour as the rear side metallization 14.
The integrated device 10 additionally contains connection legs 18, 20, which have formed a leadframe during production for example with the carrier lamina 16. In the exemplary embodiment, there is a bonding wire 22 between the integrated component 12 and the connection leg 18. There is a bonding wire 24 between the integrated component 12 and the connection leg 20. By way of example, the connection leg 18 serves as connection of a control terminal (gate). By contrast, the connection leg 20 serves e.g. as connection of an operating terminal, e.g. drain or source. The device 10 also contains a further connection leg, e.g. source or drain, respectively, which is electrically conductively connected to the carrier lamina 16.
In the exemplary embodiment, the electronic device 10 is surrounded by a housing body 26, for example by an epoxide-based housing body.
In other exemplary embodiments, a printed circuit board or a wiring arrangement produced using thin-film technology is used instead of the carrier laminae 16, 16a, 16b. As an alternative, other connection possibilities are utilized. By way of example, the integrated component 12 can be mounted onto an interposer printed circuit board or onto a main printed circuit board using flip-chip technology, that is to say, if appropriate, without the use of bonding wires.
The method steps explained below with reference to
The wafer 52 contains already integrated circuit elements, such as transistors on or in an active wafer layer 54. Said wafer layer 54 faces the carrier plate 50. By way of example, the active wafer layer 54 is protected by an imide layer. Such a layer can also serve for topology equalization.
In the exemplary embodiment, the wafer 52 is a silicon wafer. The layer thickness D2 of the wafer is for example greater than 400 micrometres, for example 750 micrometres.
In an alternative method, the carrier plate 50 is a glass plate and the so-called glass plate method from the company 3M is used. The wafer is areally connected to the glass plate, which is possibly somewhat larger than the wafer, by means of an adhesion substance, e.g. an adhesive. Possible topologies of the active wafer are embedded in the process. After the process steps that are carried out with the carrier, the adhesive connection can be separated again. In this case, an auxiliary layer previously applied to the carrier is activated with the aid of a laser. The carrier can then be removed. The adhesive layer is subsequently removed from the active wafer with the aid of a self-adhesive film.
As is illustrated in
By way of example, a three-stage thinning process is used for thinning the wafer. By way of example, the wafer is firstly thinned by means of a grinding method (not illustrated). After the grinding operation, a wet-chemical etching process is carried out, for example, in which the wafer is thinned to the vicinity of the thickness D3. Afterwards, a chemical mechanical polishing (CMP) is carried out by means of the polishing head 56 illustrated in
Before the rear side metallization 14a is applied, e.g. a doping step is additionally carried out, for example an implantation step, in order to introduce dopants into the rear side of the wafer 52a. In order to activate the dopants, the wafer 52a is heated in regions with the aid of a laser beam. This measure prevents the adhesive for adhesively bonding the carrier plate 50 onto the wafer 52a from losing its adhesive strength.
After thinning, as illustrated in
As is illustrated in
The carrier 50 is subsequently removed, for example by using a solvent, by UV irradiation or by being pulled off. In an alternative variant, the carrier 50 is removed before the composite is fixed onto an adhesive film or on a further carrier. In these cases, the carrier 50 can be stripped away for example by increasing the temperature to greater than 100° C., but less than 200° C. As an alternative or in addition, it is possible in turn to use a solvent, a UV radiation or some other method for stripping away the carrier 50. Moreover, further processing steps without the use of intermediate carriers, e.g. heat treatment of the wafers, test and inspection of the chips at the wafer level, can be carried out after the removal of the carrier plate 50 and prior to singulation.
As is further illustrated in
As is further illustrated in
In an alternative separating method, a laser beam is used for the separation. By way of example, a water-cooled laser beam can be used, the water rinsing away in particular metal detachments or swarf, such that a clean separating cut arises. An associated system is offered for example by the company Synova.
In an alterative separating operation, only one saw blade is used, which severs the entire composite.
A copper layer 14b having a layer thickness within the range of 20 micrometres to 200 micrometres was subsequently applied. In this case, the thickness of the copper layer 14b is chosen depending on the residual layer thickness of the thinned wafer 52b, such that a sufficient stability is present after the carrier plate 50 has been stripped away. In the exemplary embodiment firstly a thin copper seeding layer was sputtered onto the barrier 13b. The copper layer was subsequently produced with the aid of an electrolytic method. A copper alloy layer can also be used instead of a copper layer 14b.
A protective layer 15b or a protective layer stack was subsequently applied to the copper layer 14b. By way of example, a nickel layer and a gold layer were applied in an electroless deposition method. As an alternative, a layer stack composed of nickel, palladium, gold can be applied. Other protective layers are likewise possible. If work is carried out under a protective gas atmosphere or in vacuo, then it is also not necessary to use a protective layer 15b.
The protective layers 15b mentioned ensure a good bondability, for example for aluminium wires, copper wires or gold wires.
As an alternative, the copper layer 14b can also be laminated on, for example onto the barrier layer 13b or directly onto the silicon 52b.
The layer thickness of the thinned wafer 52b lies for example within the range of 100 nanometres to 200 micrometres, or within the range of 1 micrometre to 200 micrometres. In particular, wafers having diametres of 150 mm, 200 mm or even 300 mm are used. Depending on the thickness of the thinned wafer 52b, the layer thicknesses mentioned in Patent claim 3 are chosen for the copper layer 14b. It holds true, in particular, that the thinner the wafer 52b, the thicker the copper layer 14b is chosen in order to ensure sufficient stability.
A barrier layer 13c is applied to the rear side of the wafer 52c with the carrier plate 50 still being present. The barrier layer 13c is intended to prevent diffusion of aluminium into the silicon. By way of example, the barrier layer 13c has a layer thickness within the range of 5 nanometres to 100 nanometres. By way of example, titanium or titanium nitride or a similar material is suitable as material of the barrier layer 13c.
After the production of the barrier layer 13c, an aluminium layer 14c was applied to the barrier layer 13c, for example with the aid of a “cold” sputtering method, the wafer 52c being heated to temperatures of less than 100° C. (degrees Celsius), in particular by using an additional cooling or by other suitable measures.
After the production of the aluminium layer 14c, a protective layer 15c composed of aluminium oxide forms automatically for example under air, said protective layer having for example a layer thickness of 5 to 20 nanometres. As an alternative, other protective layers 15c composed of other materials are applied, or work is carried out under a protective gas atmosphere or in vacuo.
Instead of aluminium, an aluminium alloy is also used, for example, which contains at least 75 atomic percent of aluminium, for example.
The layer thickness of the thinned wafer 52c once again lies within the range of, for example, 100 nanometres to 200 micrometres or within the range of 1 micrometre to 200 micrometres, e.g. wafers having a diameter of 150 mm, 200 mm or 300 mm once again being used. The layer thickness of the aluminium layer 14c is chosen depending on the layer thickness of the wafer 52c, the values mentioned in Patent claim 3 being applicable. It holds true, in particular, that the thinner the wafer layer 52c, the thicker the aluminium layer 14c in order to ensure sufficient stability.
In other exemplary embodiments, bonding is effected onto the protective layer 15b or onto the protective layer 15c or other connecting methods are used for electrical connection, e.g. soldered-on wire clips or the like.
Consequently, to summarize it holds true that a rear side metallization can be used as a carrier and that the rear side metallization used as a carrier can also be concomitantly incorporated in a housing body, for example. The technical effects mentioned above result.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102006046789.2 | Oct 2006 | DE | national |
