Method for joining two wafers

0001This patent application claims the priority of German Patent applications and 102004009625.2-11 102004012013.7-33, included the disclosure of which is incorporated by reference becomes.

0002The invention relates to a method of bonding two wafers. In addition, the invention relates to a wafer assembly.

0003From document US 6,284,998 B1 discloses a method for Soldering an electronic component onto a dielectric known substrate. On one surface of the substrate purpose, at least two connection points of metal set, which are each covered with solder paste. Hereinafter the terminals of the electronic component with the brought junctions on the substrate in contact. Of the Beam of a diode laser is then so long by the Interchanges opposite side of the substrate on each directed one of the metallic connection points until the solder paste on the junction melts. The wavelength the laser beam is chosen so that the laser energy primarily from the connection point and not from dielectric substrate is absorbed. After cooling the junction is a solder joint between the terminal and the terminal of the electronic Component.

0004The publication DE 103 03 978 A1 describes a method for the manufacture of a semiconductor device in which a respectively on thin-film semiconductor body and carrier solders applied. are thin-film semiconductor body and carrier then under elevated pressure at a temperature above the Melting point of the solder metals involved is, together.

0005Object of the present invention is a method for specify as simple links two wafers. It is another object of the invention to provide a wafer assembly.

0006These objects are achieved by a method for joining two wafers according to claim 1 and further by the Wafer assembly according to claim 30 Advantageous embodiments the invention are subject of dependent claims.

0007There is provided a method for bonding two wafers. For this purpose, between the two wafers, a contact area formed by the two wafers are superposed. The connection between the wafers takes place by a local and temporary heating of the contact region of the two Wafer instead.

0008Localized heating in this context means, that a considerable heating the wafer in a direction parallel or perpendicular to the contact area, preferably in both directions, remains limited. After cooling are both Wafer then, at its contact area, at the site of local heating mechanically interconnected.

0009In one embodiment of the process two wafers are provided. is on at least one of the wafer surfaces a material applied. Here, the material on the entire wafer surface are applied distributed, or Material locally to selected areas of the wafer surface applied, or the material is over the entire applied distributed wafer surface and then from selected areas, for example etched away. Subsequently, a contact area between the Wafern'hergestellt, by the wafers are superposed, that the deposited material between the wafers is. Through a local and temporary heating the material in the contact area then creates a mechanical Connection between the wafers conveyed through the material between the wafers.

0010The material can, for example, suitably selected so be that the material by the local heating initially melts and on cooling to form a eutectic solidified with the wafer material.

0011In a further embodiment of the method in the surfaces of both wafers applied materials. there is different, the material on the first wafer is applied on the material on the second wafer is applied.

0012The materials need not necessarily to the entire Wafer surface are applied, but can also at times, Applied to selected areas of the wafer surface will.

0013The two wafers are subsequently superimposed in such a way that the materials between the wafers . are The materials are then produced in the so limited contact area between the wafers in place and time heated, so that the two different materials combine in the field of heating. This can, for example, take place in that the two materials melt and the material in the molten mix. Also an increased mobility of the particles due to the Warming is conceivable so that by particle diffusion a Mixing of the materials takes place.

0014In any case arises after the place and time limited Heating the contact region a mechanical connection between the wafers, mediated by the materials between the wafers.

0015In a preferred embodiment of the invention, , the materials, the most on the wafer surfaces Contact area be applied to solders.

0016In a particularly preferred embodiment, itself. to the perpendiculars to solders Registered find Preferably following solders in the process application: Au, AuSn, Pd, In, Pt.

0017When local heating of the contact area melts this Solders and mingle. After cooling and solidification, the solder layer then there is a mechanical connection between the wafers.

0018In a preferred embodiment of the method for connecting two wafers, the contact area between the wafers locally heated by at least one laser beam. For the principle of the method, it is immaterial whether a single laser beam in a time sequence, Centre for Place, or about a plurality of laser beams simultaneously at different locations of the contact region for use come.

0019The wavelength of the laser and at least one of the wafers are so adapted to one another that at least one of Wafer at least partially transparent to the laser beam is. This means that, at most, a slight absorption the energy of the laser beam in the wafer takes place.

0020The laser beam is then passed through at least one wafer passing focused on the area of ​​contact between the wafers.

0021The laser beam is, in a particularly preferred embodiment, a predominant extent of the material or Materials at the contact portion between the wafers absorbed. This can happen, for example, characterized in that the materials the contact area of ​​the laser beam mostly not are transparent and absorb the energy of the laser beam. This ensures that the contact area is heated is specifically localized around the area, to is directed to the focus of the laser beam. The performance the laser is to be chosen preferably high enough, so that after cooling a mechanical connection of the two Wafer is carried out at the contact area.

0022In one embodiment of the method, the laser is be operated in continuous operation.

0023For a preferred embodiment of the process is an Laser in pulsed operation appropriately. A corresponding Choice of pulse duration and pulse interval of the can Removal of the resulting heat at the contact area optimally be adjusted. So it can with a laser in Pulse mode, the geographical boundaries of the heating particularly be easily achieved. The desired time limit the heating is at a pulse-operated laser by given the limited pulse duration. For generating the laser beams comes here in a possible embodiment of the Process, a Nd: YAG laser is used.

0024In a further embodiment of the method described , the laser beam continuously over the entire contact area out between the wafers. In this way, all aspects of the contact region are locally limited heated and there is over the entire contact area both wafer, a flat, mechanical connection between the two wafers. The local heatings of Contact area, can be added in chronological order through a carried single laser beam or, when using a Plurality of laser beams at a plurality of local areas of the Contact area simultaneously.

0025In another embodiment of the method, the laser is performed on selected areas of the contact area, so that only in these selected areas to connect is made between the two wafers. It is in this case So a connection between two wafers in selected Points of the contact area achieved while other areas the contact area between the wafers without being affected by direct Heating produced compound remain. It can form, Arrangement, number and size of the connecting portions and the connectionless areas depending on the needs of be designed product. That is, shape, location, number and size of connection portions and connection-free areas, for example, of the required temperature resistance, the preferred mechanical stability, the operation of the device, adjusted or the desired cost of the product will.

0026Also in this embodiment of the process it is natural possible a single laser beam or a plurality use of laser beams.

0027In a further embodiment of the method, the Connecting both wafer at contact area pointwise. To the laser beam at the individual predetermined points the contact area focused. In these places there is thereby a connection between the two wafers. there the individual connection points to the beneficial Nodes of a regular network are arranged. Number of connection points and design of the network can be adapted to the requirements of the product.

0028Also in this embodiment, it is possible a laser beam in time series or a plurality of lasers use simultaneously. In particular, it is possible here, that the number of laser beams of the number of points desired compound equivalent.

0029In a particularly preferred embodiment of the method only to those areas of the contact area material applied, which are then irradiated by the laser beam. For example, for the case of a pointwise connection both wafer only at these points previously deposited material.

0030contains, in one embodiment of the process described at least one of the wafer is a semiconductor material.

0031In a further embodiment of the method for connecting two wafers, containing at least one of the wafers of the following semiconductor materials: silicon, germanium, gallium arsenide, InP, GaP.

0032In one embodiment, the method comprises at least a wafer at least one of the following metals: Mo, Cu, CuW. Also, at least one of the wafers in another Embodiment of the process ceramic materials included.

0033In one embodiment, the method comprises at least one of the wafer a plurality of individual layers, wherein at least one of the individual layers an epitaxially deposited Layer.

0034In a further embodiment of the method includes the epitaxially deposited layer is preferably one of the following Semiconductor materials: GaInN, AlGaAs, AlGaInP, GaP, InP, InGaAs, InGaAsP, GaN, AlGaInN.

0035Thereby forming in a preferred embodiment of the method at least a single layer of the wafer, an electronic or microelectronic component.

0036Here, embodiments are particularly preferred in which the electronic component, an optoelectronic component forms, for example, a light emitting diode, a semiconductor laser or a detector (eg photodiode).

0037Further, the invention relates to a wafer assembly, wherein two superimposed wafers at selected areas of its are contact region connected to one another.

0038This connection can, for example, by a material, or conveys two different materials between the wafer will.

0039The wafer assembly is based on the idea that the connection of the two wafers not over the entire contact area extends both wafer surface but the two Wafer only at selected points of its contact region together are connected. Thereby, the materials that the provide connection between the wafers, either in whole Contact area to be applied, or only at those locations the contact area at which a connection between the wafers is.

0040In one embodiment, the wafer arrangement, the two Wafer at its contact area pointwise, at connection points, connected with each other. Here, the sum of the areas of the contact region, at which the two wafers with each other are connected, small compared with the sum of the areas of Contact region in which no connection between the two Wafers is.

0041are in a preferred embodiment, the wafer assembly thereby the connecting points at the nodes of a regular Network arranged.

0042In a particularly preferred embodiment of the described Wafer assembly includes at least one of the wafers a particularly temperature-sensitive layer. It means that the maximum temperature to which said layer without damage can be heated, is less than, for example, the temperature at which the materials at the contact portion together. In this case would heating throughout the wafer assembly to the temperature at which connect the materials, the temperature-sensitive damage layer.

0043Next, the method described herein are for connecting two wafers and the wafer assembly described with reference embodiments and the associated figures explained in more detail:<sl><li>Figure 1 shows a schematic diagram of the described herein A method for connecting two wafers on the basis of production an AlGaInP thin-film light-emitting diode.</li><li>Figure 2 shows a schematic plan view of the contact area the wafer assembly described herein, in which the soldering of the two wafers at selected regions of the Contact area is.</li><li>Figure 3 shows a plan view of the contact area of ​​the described herein wafer assembly with pointwise soldering both wafers.</li></sl>

0044Figure 1 illustrates a method for preparing a AlGaInP Thin-film light-emitting diode 10. For this purpose, for example, be a GaAs Support wafer 11 and epitaxial wafer 12 having a AlGaInP Light emitting layer epitaxially grown on a GaAs substrate is applied, provided.

0045On the support wafer 11 is on the top, for example, an Au-Sn solder layer 13 is applied. In the epitaxial wafer 12 is on the bottom, for example, an Au layer of solder 14 applied. The solder layers 13, 14, the surfaces the respective wafers 11, 12 thereby completely cover or applied only to certain areas of the wafer surfaces will. For the method described, it is of course irrespective of the nature of the solders on which of the two Wafer is applied.

0046Then, a by superimposing the two wafer created the contact region 15, so that the solder layers 13, 14 are located between the two wafers 11, 12 and touching each other.

0047The laser beam 16, for example a Nd: YAG laser is, then at a wavelength through the support wafer 11 irradiated, wherein the carrier wafer 11 to the laser beam 16 permeable. The laser beam 16 is on the contact area 15 between the two wafers focused. However, it is also possible that the laser beam 16 through the epitaxial wafer 12 on the contact layer is focused 15th

0048The power of the laser is selected to ensure that the two Solder layers 13, 14 melt locally to the focus of the laser around, so connect the two solders together and after cooling and solidification of the locally heated region 17 a local solder connection between the two wafers 11 and 12 there. The laser can be used both in continuous operation, as well as pulsed operate.

0049Thereby, the laser beam continuously over the entire out contact region 15, the result is a flat solder between the two wafers 11, 12th

0050It is understood that in addition to the aforementioned GaAs wafer also other carrier wafer come into consideration. It is possible, for example, also the use of wafers, germanium or Silicon include. If necessary, then the wavelength of the laser beam adjusted so that the carrier wafer is at least partially transparent to the laser beam.

0051Also in the choice of the epitaxial wafer, there are numerous possibilities. Thus, the epitaxial wafer for example, a Laser diode layer or comprise a detection layer. Especially is the specified method for soldering temperature sensitive components suitable as the heating not the entire wafer arrangement, but only a locally relates limited range 17th

0052Also, the method described is in the choice of not limited solders. Since in the method described the heat load locally on the contact area between the Wafers is limited, in particular combinations of Solders conceivable that only at much higher temperatures than the dates indicated on Au and AuSn solder join.

0053After bonding of the two wafers 11, 12, the wafer assembly to individual components - for example, individual LED chips - are separated. This can, for example, effected by means of sawing or breaking the array. The finished Component can electrically from the side of the carrier wafer 11 fro be contacted. Preferably, the solders 13, 14 then electrically conductive.

0054Figure 2 shows a schematic plan view of the contact area 15 between two wafers. The two wafers are only compound selected regions 21 of the contact region 15 soldered together. find In addition to connecting areas 21 Also connectionless regions 22 of the contact area 15, at which connections between the two wafers consists.

0055It is possible that solders either only at the joining portions 21 applied to the wafer, or the Solders over the entire contact area 15 distributed applying the wafer surfaces.

0056Shape, size, number and arrangement of the compound selected areas 21 and the non-bonded regions 22 can In this case, depending on the requirements of the wafer assembly, adapted will.

0057Figure 3 shows a plan view of the contact region 15 of the here described wafer assembly. In this case, the two wafers at connection points 31 of the contact portion 15 to each other connected. The connection points 31 are at the Nodes of a regular network arranged. The connectionless Area 32 takes on a much larger area of the contact portion 15 a, than the total area of ​​the connection points 31 is.

0058It is possible the solders either only at the connection points 31 applied to the wafer, or the solders over the entire contact area 15 on the wafer surfaces apply.

0059Number and arrangement of the connection points 31 in that case to the requirements of the wafer arrangement and the requirements of the manufactured component adapted. After separation the Waferanordung can in this embodiment, components result, from the side of the carrier wafer 11 are her only point-wise electrically contacted.

0060Since, in a point-wise connection of the two wafers, the temperature load is particularly low, this wafer assembly for example particularly suitable when at least one of the wafers a temperature-sensitive component includes. Because with pointwise bonding the two wafers place a small only a few places the wafer assembly Temperature entry in the wafer instead and the overall temperature record is very low.

0061It is in the latter two embodiments possible per connection point 31 or per connection area 21 exactly one component results. This means, it is possible that, for example, places where the wafer assembly to be isolated (eg, predetermined breaking points or Sägekanäle), the wafers 11, 12 with each other non- get connected. Only where devices are formed should be found, the connection of the two wafers 11, 12 instead of.

0062The invention is not by the description on the basis of Embodiments limited. Rather, the invention comprises any new feature and any combination of features, in particular any combination of features in the patent claims includes, even if this feature or this Combination itself is not explicitly in the claims or embodiments indicated.