Method for joining two wafers

p0001The invention relates to a method of bonding two wafers.

p0002The documents <patcit id="pcit0001" dnum="WO0219439A"><text>WO 02/19439</text></patcit> and <patcit id="pcit0002" dnum="US20040033638A"><text>US 2004/0033638</text></patcit> describe optoelectronic devices manufactured by bonding two wafers.

p0003The publication <patcit id="pcit0003" dnum="US6284998B1"><text>US 6284998 B1</text></patcit> discloses a method for soldering an electronic component on a dielectric substrate. at least two connection points are given to metal, which are each covered with solder paste on a surface of the substrate. In the following, the terminals of the electronic component are contacted with the connection points on the substrate in contact. The beam of a diode laser is then directed through the long, the connection points opposite side of the substrate on each one of the metallic connection points, until the solder melts at the connection point. The wavelength of the laser beam is chosen so that the laser energy is mainly not absorbed by the connection point and the dielectric substrate. After cooling the junction there is a solder connection between the terminal and the terminal of the electronic component.

p0004The document <patcit id="pcit0004" dnum="DE10303978A1"><text>DE 103 03 978 A1</text></patcit> describes a method for producing a semiconductor device.

p0005The documents <patcit id="pcit0005" dnum="DE4219132A1"><text>DE 4219132 A1</text></patcit> and <patcit id="pcit0006" dnum="US20010014514A1"><text>US 2001/0014514 A1</text></patcit> describe methods for joining two wafers. The documents<patcit id="pcit0007" dnum="US5460318A"><text>US 5.460318</text></patcit>. <patcit id="pcit0008" dnum="WO2004015756A1"><text>WO 2004/015756 A1</text></patcit> and <patcit id="pcit0009" dnum="US5481082A"><text>US 5,481,082</text></patcit> describe methods for applying individual optoelectronic components on the carrier.

p0006The object of the present invention is to provide a method for easily possible connecting two wafers. It is another object of the invention to provide a wafer assembly.

p0007These objects are achieved by a method of bonding two wafers according to claim 1. Advantageous embodiments of the invention are subject matter of subclaims.

p0008There is provided a method for bonding two wafers. For this purpose, a contact area is formed by the two wafers are superposed on each other between the two wafers. The connection between the wafers takes place by a local and time limited heating of the contact area of ​​the two wafers.

p0009Localized 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 both wafers are then at their contact area, mechanically interconnected at the site of local heating.

p0010In one embodiment of the process two wafers are provided. At least one of the wafer surfaces, a material is applied. The material can be applied distributed over the entire wafer surface, or the material is locally applied to selected areas of the wafer surface, or the material is distributed over the entire wafer surface applied and then removed from selected areas, for example etched away. Subsequently, a contact area between the Wafern'hergestellt by the wafers are overlaid so that the applied material is between the wafers. By a local and time limited heating of the material in the contact area then creates a mechanical connection between the wafers conveyed through the material between the wafers.

p0011The material can be selected, for example, suitable as the material first melted by local heating and solidifies on cooling to form a eutectic with the wafer material.

p0012In a further embodiment of the process materials are applied to the surfaces of both wafers. Here, the material that is applied to the first wafer is different from the material that is applied to the second wafer.

p0013The materials must not be applied strictly on the entire wafer surface, but can also at times be applied to selected areas of the wafer surface.

p0014The two wafers are subsequently superimposed in such a way that the materials between the wafers are. The materials are then heated locally and temporally limited thus produced contact area between the wafers so that connect the two different materials in the field of heating. This can occur, for example, that the two materials melt and mix the material in the melt. Also an increased mobility of the particles due to heating is conceivable so that by particle diffusion takes place a mixing of materials.

p0015In any case, after the local and time limited heating of the contact area results in a mechanical connection between the wafers, mediated by the materials between the wafers.

p0016In a preferred embodiment of the invention, the materials, which are applied to the wafer surfaces to the contact area to solders.

p0017In a particularly preferred embodiment, when the solder to solder metals. Registered find Preferably, the following solders in the process application: Au, AuSn, Pd, In, Pt.

p0018When local heating of the contact area, these solders melt and mingle. After cooling and solidification of the solder layer then there is a mechanical connection between the wafers.

p0019In a preferred embodiment of the method for bonding two wafers, the contact area between the wafers by means of at least one laser beam is locally heated. For the principle of the method, it is irrelevant whether a single laser beam in a time sequence, digit by digit, or about a plurality of laser beams are used simultaneously at different points of the contact area for use.

p0020The wavelength of the laser and at least one of the wafers are so adapted to one another that at least one of the wafer for the laser beam is at least partially permeable. This means that, at most a slight absorption of the energy of the laser beam takes place in the wafer.

p0021The laser beam is then focused through the wafer to the contact area between the wafers by at least one.

p0022The laser beam is absorbed in a particularly preferred embodiment, to a predominant extent of the material or materials at the contact portion between the wafers. This can for example take place in that the materials at the contact area of ​​the laser beam are not predominantly transparent and absorb the energy of the laser beam. This ensures that the contact area is heated and although limited locally around the area on which the focus of the laser beam is directed. The power of the laser is to be chosen preferably sufficiently high so that after cooling a mechanical connection of the two wafers is carried out at the contact area.

p0023In one embodiment, the method of the laser can be operated in continuous operation.

p0024For a preferred embodiment of the method a laser in pulsed operation is appropriate. can be optimally set by appropriate selection of the pulse duration and pulse interval thereby the removal of the generated heat at the contact surface. It can thus the geographical boundaries of the heating are particularly easily achieved with a laser in pulsed operation. The desired time limit of heating is given in a pulse-operated laser by the limited pulse duration. For generating the laser beams is employed in a possible embodiment of the process, a Nd: YAG laser is used.

p0025In a further embodiment of the process described, the laser beam is guided continuously over the entire area of ​​contact between the wafers. In this manner, all areas of the contact region are heated locally, and it is formed over the entire contact area of ​​both wafer-scale a mechanical connection between the two wafers. The local heatings of the contact area, can be carried out in time sequence by a single laser beam, or, when using a plurality of laser beams at a plurality of local areas of the contact region at the same time.

p0026In another embodiment of the method, the laser is guided over selected areas of the contact region, so that only in these selected areas a connection between the two wafers is made. It thus a connection between the two wafers is achieved in selected locations of the contact area, while other areas of the contact region between the wafers remain without prepared by direct heating compound. In this form, arrangement, number and size of the connecting portions and the connection-free areas can be designed according to the requirements of the product. That is, shape, location, number and size of connection portions and non-bonded areas can, for example, the required temperature resistance, the preferred mechanical stability, the functioning of the device, or the desired cost of the product to be adapted.

p0027Also in this embodiment of the process it is of course possible to use a single laser beam or a plurality of laser beams.

p0028In a further embodiment of the process combining the two wafers is pointwise at the contact area. For this, the laser beam is focused at the individual predetermined points of the contact area. At these points, this results in a connection between the two wafers. Here, the individual connection points can be arranged advantageously at the nodal points of a regular network. Number of Binding and configuration of the network can be adapted to the requirements of the product.

p0029Also in this embodiment, it is possible to employ a laser beam in a time sequence or a plurality of lasers simultaneously. In particular, it is possible here that the number of laser beams of the number of the desired connection points corresponds.

p0030In a particularly preferred embodiment of the method material is applied only to those areas of the contact region, which are then irradiated by the laser beam. For example, previously material is applied for the case of point-point connection of both wafer only at these points.

p0031In one embodiment, the method described at least one of the wafer includes a semiconductor material.

p0032In a further embodiment of the method for bonding two wafers, at least one of the wafers includes one of the following semiconductor materials: silicon, germanium, gallium arsenide, InP, GaP.

p0033In one embodiment of the method, at least one of the wafers contains at least one of the following metals: Mo, Cu, CuW. Also, at least one of the wafers in a further embodiment of the method of ceramic materials.

p0034In one embodiment, the method comprises at least one of the wafer a plurality of individual layers, where one of the individual layers is at least one epitaxially deposited layer.

p0035In a further embodiment of the method, the epitaxially deposited layer preferably comprises one of the following semiconductor materials: GaInN, AlGaAs, AlGaInP, GaP, InP, InGaAs, InGaAsP, GaN, AlGaInN.

p0036In this case, in a preferred embodiment of the process forms at least a single layer of the wafer, an electronic or microelectronic device.

p0037Here, embodiments are particularly preferred in which the electronic component forming an optoelectronic component, for example a light emitting diode, a semiconductor laser or a detector (eg photodiode).

p0038Further, a wafer arrangement in which two superimposed wafers are joined at selected areas of their contact area, as described, which is not part of the invention.

p0039This connection can, for example, by a material or two different materials are conveyed between the wafer.

p0040The wafer assembly is based on the idea that does not extend the connection of the two wafer over the entire contact area of ​​both wafer surface but the two wafers are joined together only at selected locations of their contact area. Thereby, the materials which provide the connection between the wafers, either be applied in the entire contact area, or only at those points of the contact region in which there is a connection between the wafers.

p0041In one embodiment, the wafer arrangement, the two wafers are pointwise at its contact area, at connection points, connected to each other. Here, the sum of the areas of the contact region, at which the two wafers are joined together, small relative to the sum of the areas of the contact region in which there is no connection between the two wafers.

p0042In a preferred embodiment, the wafer arrangement, the connection points are arranged at the nodes of a regular network.

p0043In a particularly preferred embodiment, the wafer-described arrangement, at least one of the wafers includes a particularly temperature-sensitive layer. That is, the maximum temperature to which this layer can be heated without damage, is less than for example, the temperature at which the materials at the contact region together. In that case, heating the entire wafer arrangement on the temperature at which to connect the materials, damage the temperature-sensitive layer.

p0044Next, the method described herein for connecting two wafers and wafer described arrangement will be explained with reference to embodiments and the associated figures:<ul><li><figref idrefs="f0001">figure 1</figref> shows a schematic diagram of the process described herein for connecting two wafers on the basis of the preparation of a AlGaInP thin-film light-emitting diode.</li><li><figref idrefs="f0002">figure 2</figref> shows a schematic plan view of the contact region of the wafer assembly described herein, in which the soldering of the two wafers is at selected areas of the contact region.</li><li><figref idrefs="f0002">figure 3</figref> shows a plan view of the contact area of ​​the wafer assembly described herein in pointwise soldering of both wafers.</li></ul>

p0045<figref idrefs="f0001">figure 1</figref> illustrates a method for preparing a thin film AlGaInP light-emitting diode 10. For this purpose, a GaAs carrier wafer 11 and an epitaxial wafer 12 are light-emitting diodes with an AlGaInP layer, which is epitaxially deposited on a GaAs substrate provided, for example.

p0046On the support wafer 11, for example, an Au-Sn solder layer 13 is applied on top. In the epitaxial wafer 12 is applied, for example, an Au-solder layer 14 to the bottom. The solder layers 13, 14, the surfaces of the respective wafers 11, 12 is completely covered, or only be applied to certain areas of the wafer surfaces. For the method described, it is of course of no importance, the solders will be applied to which of the two wafers.

p0047Then, a contact area 15 is generated by the superposition of the two wafers, so that the solder layers 13, 14 between the two wafers 11, 12 are and touching each other.

p0048The laser beam 16, for example, an Nd: YAG laser is then irradiated at a wavelength through the support wafer 11, wherein the carrier wafer 11 is transparent to the laser beam 16th The laser beam 16 is focused on the contact area 15 between the two wafers. However, it is also possible that the laser beam 16 is focused by the epitaxial wafer 12 through the contact layer 15th

p0049The power of the laser is for chosen so that the two solder layers 13, 14 melt locally to the focus of the laser around, so that connect the two solders each other and, after cooling and solidification of the locally heated region 17, a local solder connection between the two wafers 11 and 12 is made. The laser can be operated in pulsed mode, both in continuous operation when.

p0050The laser beam is guided continuously over the entire contact area 15, the result is a flat solder connection between the two wafers 11, 12th

p0051It will be understood that come adjacent to said GaAs wafer also other carrier wafer into account. the use of wafers, the germanium or silicon is possible, for example, include. Optionally, the wavelength of the laser beam is then adjusted so that the support wafer for the laser beam is at least partially transparent.

p0052Also in the choice of the epitaxial wafer, there are numerous possibilities. Thus, the epitaxial wafer for example, contain a laser diode layer or a detection layer. In particular, the method given for the brazing is suitable for temperature sensitive components, as the heating does not affect the entire wafer arrangement, but only a localized area 17th

p0053Also, the method described with regard to the choice of the solders is not limited. Since the heat load is limited locally to the contact area between the wafers in the process described, in particular combinations of solders are conceivable that combine only at much higher temperatures than the dates indicated on Au and AuSn solder.

p0054After joining the two wafers 11, 12, the wafer assembly may be individual components - for example, each LED chip - are separated. This can be done for example, by sawing or breaking of the assembly. The finished component can be contacted from the side of the carrier wafer 11 fro electrically. Preferably, the solders 13, 14 are then electrically conductive.

p0055<figref idrefs="f0002">figure 2</figref> shows a schematic plan view of the contact area 15 between the two wafers. The two wafers are soldered together only at selected areas 21 connecting the contact region 15th In addition to the connection portions 21, there are also connectionless regions 22 of the contact region 15, where there is no connection between the two wafers.

p0056It is possible to either apply the solder metals only at the joining portions 21 on the wafer, or the solder metals over the entire contact area 15 is distributed to be applied to the wafer surfaces.

p0057Shape, size, number and arrangement of the compound selected regions 21 and the non-bonded regions 22 can thereby, depending on the requirements of the wafer assembly, adjusted.

p0058<figref idrefs="f0002">figure 3</figref> shows a plan view of the contact area 15 of the wafer assembly described herein. In this case, the two wafers at connection points 31 of the contact portion 15 are connected together. The connection points 31 are arranged at the nodes of a regular network. The compound-free region 32 takes on a far greater area of ​​the contact region 15, than the total area of ​​the connecting points is the 31st

p0059It is possible to apply the solder metals either only at the connection points 31 on the wafer, or to apply the solder metals over the entire contact area 15 on the wafer surfaces.

p0060Number and arrangement of the connection points 31 are adapted to the requirements of the wafer arrangement and the requirements for the manufactured component. After separation of Waferanordung components can in this embodiment arise that are contacted by the side of the carrier wafer 11 forth at certain points only electrically.

p0061Since, the thermal stress is particularly low at a pointwise connection of both wafer, this wafer arrangement is for example particularly suitable when at least one of the wafers includes a temperature-sensitive component. Because with pointwise bonding the two wafers takes only a few places the wafer assembly a low temperature record in the wafer instead and the overall temperature entry is very low.

p0062It is also possible in the latter two embodiments, that exactly per connection point 31 or per connection portion 21 results in a component. That is, it is possible that, for example, places where the wafer assembly is to be isolated (eg, predetermined breaking points or Sägekanäle), the wafers 11, 12 are not connected together. Only where components are to be created, then joining the two wafers 11, 12 takes place.