DE10017336C2 - Process for the production of radiation-emitting semiconductor wafers - Google Patents

Description

The invention relates to a method for producing radiation-emitting Semiconductor wafers according to claim 1.

Radiation-emitting diodes (LEDs) are known which are based on AlInGaP using MOVPE (Metal Organic Vapor Phase Epitaxy) on GaAs are upset. The GaAs semiconductor substrate, however, is the emissive Absorbing wavelength and has poor thermal conductivity λ = 0.54 W / K.cm. Because in particular light emitting diodes due to their high Lifespan increased in daylight applications, especially in Motor vehicle in which brake lights are used as a replacement for a light bulb you need high light outputs. To achieve high light outputs with conventional To achieve technology, all causes of absorption must be eliminated. Out for this reason, when building radiation-emitting semiconductor Wafers currently use two different techniques. For one, one can Bragg reflector between semiconductor substrate and radiation emitting Layers are used or the absorbent GaAs semiconductor The substrate is replaced by a transparent GaP semiconductor substrate.

The disadvantage here, however, is that the semiconductor substrates used are very are expensive and do not always have all the required properties. In particular, the GaP semiconductor substrate only conducts the power loss poorly and the LED heats up strongly in high-performance operation. The thermal conductivity of GaP is also only λ = 1.1 W / K.cm. Thereby the light output is limited and if it heats up too much, a  Wavelength shift take place. Large layer thicknesses (approx. 200-300 µm) of the GaP substrate is required. Therefore, low heights are not realizable. The large layer thickness also increases the thermal Resistance.

Methods are known from EP 0 616 376 A1 and EP 0 356 037 B1 which refer to the top of a wafer, which has the original on its underside Has substrate, attach another semiconductor substrate. The attachment is done by the so-called wafer bonding. After wafer bonding it will original substrate removed.

The disadvantage here, however, is that high temperatures and above all, a high contact pressure is required. This causes high levels in the wafer generates mechanical stresses and the light-emitting layers can be damaged or destroyed. The process times for wafer bonding are also very long. Another disadvantage arises from the complex adjustment of the Crystal axes in wafer bonding.

From the IEEE Photonics Technology Letters, Vol. 10, No. August 8, 1998, page 1061; Grabherr, M. and others: 'Bottom-Emitting VCSEL's for High-CW Optical Output Power 'is a structure known in which on a GaAs substrate photosensitive layers have grown. There is one on it Solder layer. Here the component is soldered to a heat sink, which consists of a Layer of diamond and a layer of copper. The radiation emerges over the GaAs substrate. The light-sensitive layers are partly in the Solder layer embedded.

Disadvantages arise with this structure in that the structure is very high and mechanical stresses on the semiconductor when soldering into the heat sink occur due to force on the side walls and the wafer high Exposed to temperatures, so that the degradation increases.

From Electronics Letters, Vol. 33, No. 13, 19 ^th June 1997, page 1148-1149; Matsuo, S. and others: 'Use of polyimide bonding for hybrid integration of a vertical cavity surface emitting laser on a silicon substrat' also discloses a laser arrangement in which light-sensitive layers are applied to a GaAs substrate and are embedded in Bragg reflectors , A mechanical buffer is a polyimide layer on the top Bragg reflector layer. An additional silicon substrate, on which gold contacts are partially formed, is connected to this layer by bonding. The light-sensitive layers with the Bragg reflectors are completely embedded in the polyimide layer. The original GaAs substrate is finally removed.

The disadvantage here is that the polyimide that completely surrounds the semiconductor Exerts tension on it and thereby increases the degradation. Another The disadvantage is the high structure of the arrangement, which makes the lower one Contact cannot be brought all the way to the surface of the body. Furthermore, the silicon substrate has a high thermal resistance.

JP 8-88410 A discloses a semiconductor element, the underside of which is exposed, whereby the light output can be increased. Furthermore, the Underside a peripherally arranged underside contact. The bottom contact and its immediate surroundings is through a glued metal plate strengthened.

The disadvantage here, however, is that the reinforcement is only arranged in a ring, which creates mechanical stability at the center of the semiconductor device is worse than outdoors.

The object of the invention is therefore to provide a method of the type mentioned to demonstrate with the radiation-emitting flat, low degradation Semiconductor devices can be manufactured that are both high Luminous efficiency, as well as good heat dissipation in high-performance operation have and with which an inexpensive production is guaranteed.

The object is achieved by the features in the characteristic of Claim 1 solved. Here is a process for the production of radiation-emitting semiconductor wafers disclosed, in which the carrier substrate, with the desired properties on which semiconductor wafers are glued. The semiconductor wafer still shows the original when glued together Substrate, which is located on the side facing away from the carrier substrate.  

Before the semiconductor wafer and carrier substrate are bonded, the surface is on top of the epitaxial layer of the semiconductor device with a all-over or partial metallization.

Advantageous developments of the invention result from the dependent claims. In these, the semiconductor structure is provided with a reflective metallization. The carrier substrate is also covered on one side with a metallization. If the two parts are glued together at their metallization, the radiation generated in the active part, which reaches the upper epitaxial layer, is reflected back. The metallization can also simplify the formation of the contact surfaces, provided that the carrier substrate itself is not already metallic. In a further embodiment, a material with a higher thermal conductivity λ <1.1 W / K.cm, in particular ceramic, silicon carbide (SiC) or sapphire (Al ₂ O ₃ ), is used as the carrier substrate, so that the semiconductor components with higher currents operated and higher light outputs can be achieved without undesirable side effects such as wavelength shift, stagnation of light output and reduction in life expectancy.

The advantages of the invention are the simple and inexpensive manufacture flat, bright and low-degradation, radiation-emitting components. The fact that the carrier substrate is already applied before the original substrate is removed, the wafer is very suitable for further processing stable. An additional mechanical buffer layer is no longer required. Also various substances can be selected for the carrier substrate, regardless of whether it is a conductor, semiconductor or insulator. Here are the properties such as thermal conductivity, Radiation conductivity, reflectivity of the carrier substrate and the Connection between carrier substrate and window layer chosen so that higher Radiant powers can be achieved. Also through such Structure the lifespan of the components compared to similar structures be enlarged. Likewise, the carrier substrate can be made flatter, so that this method is particularly thin semiconductor devices have it made. In particular, a mechanically stable carrier substrate allows a smaller substrate thickness than the known radiation-emitting diodes on transparent GaP substrate. Also due to the thinner substrate structure the thermal resistance of the component can be significantly reduced.

The invention is intended to be described in the following with the aid of exemplary embodiments and figures are explained in more detail. Show it:

Fig. 1: layer structure of the radiation-emitting semiconductor structure before assembly on an insulator;

FIG. 2a: Metallization of semiconductor wafer and the carrier substrate;

FIG. 2b: adhesive bonding of semiconductor wafer and the carrier substrate with a conductive adhesive;

Fig. 2c: removing the original substrate;

Fig. 2d: patterning of the light-active portion;

Fig. 2e: separation of the front and rear contacts;

Fig. 2f: passivation;

Fig. 2g: formation of the contacts;

Fig. 2h: separation;

Fig. 3: cross section through a radiation-emitting semiconductor component with a subsequently applied support substrate;

Fig. 4 is a top view of a radiation-emitting semiconductor component with a subsequently applied support substrate;

Fig. 5: Gluing the semiconductor wafer and carrier substrate with insulating adhesive.

Fig. 1 shows the layer structure of the radiation-emitting semiconductor structure prior to assembly on a supporting substrate. To produce such a semiconductor structure, the structure with the photoactive layers is first grown on a GaAs substrate by means of MOVPE or another method, as in conventional LEDs (light-emitting diode). The thickness of the GaAs substrate 1 is approximately 350 μm. After suitable intermediate layers, which are not shown, a so-called stop layer 2 is grown on the substrate, which should later enable the substrate 1 to be selectively removed from the layers 3 , 4 , 5 , 6 , 7 , 8 grown over it. The thickness of the stop layer 2 , which consists of Al _0.5 Ga _0.5 As, is approximately 0.5 µm. A highly doped, transparent contacting layer 3 , in particular n ++ Ga _0.75 In _0.25 P, is subsequently grown, to which the contacts are later applied on the radiation-emitting side. The thickness of this contacting layer is approximately 0.02 µm. Then a so-called "spreading" layer 4 , which is to be referred to below as a current distribution layer, is applied from highly doped n ++ (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P, which ensures a favorable current distribution and its layer thickness in the range of approximately 1-2 µm. An approximately 0.5 µm thick cladding layer 5 made of n + (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P is applied thereon. The layer thereon is the actual photoactive layer 6 made of AlGaInP. On top of this is the second 0.5 µm thick cladding layer 7 made of p + (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P. On top of this, for technological reasons, a window layer 8 made of p ++ GaP is used to improve the coupling out of light and for mechanical buffering grown with a layer thickness in the range of approx. 3-6 µm, to which a reflective metallization is later applied, which at the same time ensures contact with the carrier substrate to be attached later. A semiconductor wafer with such a layer structure forms the basis for the method shown in FIGS. 2a-h.

Fig. 2a shows the metallization of semiconductor wafer and the carrier substrate. It represents the first step for the process for producing radiation-emitting semiconductor components with a thermally conductive carrier substrate. Here, the front of a second substrate 9 , hereinafter referred to as the carrier substrate, with a well-adhering metallization 10 , in particular Ti, Pd, Ag or Mixtures thereof. The carrier substrate is characterized in that, for example, it has better thermal conductivity than GaP with λ <1.1 W / K.cm. Its thickness is also only approx. 100 µm. Likewise, the epitaxial side - that is, the window layer 8 - of the semiconductor wafer, as shown in FIG. 1, is provided with a reflective metallization 11 , for example made of Au, Zn, Ag, Ge, Ni or mixtures thereof. This reflective metallization 11 has two functions. On the one hand it ensures ohmic contact and a highly reflective surface and on the other hand it is suitable for gluing to the metallized carrier substrate 10 using a suitable adhesive such as polyimide or silicone. In the application example, an electrically conductive adhesive such as. B. Ag-filled polyimide is used, which forms an electrically conductive connection layer together with the metallizations, but this is not necessarily the case.

FIG. 2b shows the connection of semiconductor wafer and the carrier substrate. In this second step, the carrier substrate 9 and the window layer 8 of the semiconductor wafer, as shown in FIG. 1, are bonded to the two metallized sides 10 and 11 . This process should take place at low pressures and low temperatures in order to induce as little stress as possible. The adhesive layer 13 connects the metallized semiconductor wafer and the new carrier substrate 9 . In this application example, Ag-filled polyimide is used as the adhesive. This adhesive is conductive and not transparent.

Thereafter, as shown in FIG. 2c, the previous GaAs substrate 1 is selectively removed up to the etch stop layer 2 . By removing the etch stop layer 2 , the highly doped contact layer 3 is exposed. The resulting new wafer now consists of a carrier 9 which has a very good thermal conductivity, an adhesive layer 13 which is arranged between two metallization layers 10 , 11 and a radiation-emitting semiconductor structure 12 . The radiation-emitting semiconductor structure 12 in turn is composed of a window layer 8 made of p ++ GaP with a layer thickness in the range of approximately 3-6 μm. On this there is a 0.5 µm thick cladding layer 7 made of p + (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P. The layer on top is the actual photoactive layer 6 made of AlGaInP. There is a further approximately 0.5 µm thick cladding layer 5 made of n + (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P. After this, the current distribution layer 4 made of highly doped n ++ (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P is arranged, which ensures a favorable current distribution and whose layer thickness is in the range of approx. 1-2 µm. At the very top is the highly doped, transparent contacting layer 3 , in particular made of n ++ Ga _0.75 in _0.25 P. The thickness of this contacting layer is approximately 0.02 µm.

In the subsequent fourth step, as shown in FIG. 2d, the active area of the structure is determined by a mesa etching. The radiation-emitting semiconductor structure 12 with all layers ( 3 , 4 , 5 , 6 , 7 , 8 ) is partially removed down to the metallization 10 , since the elastic conductive adhesive layer 13 and the reflective metallization 11 of the semiconductor structure arranged above it for later bonding of the component are not suitable. As a result, the remaining radiation-emitting semiconductor structure 12 is structured and the active area of the individual components 21 that are created later is defined.

The etching shown schematically in FIG. 2e leads to the electrical isolation of the front 14 and rear 15 contacts . In this case, the metallization layer 10 is structured through, that is to say the metallization of the carrier substrate 10 is partially removed down to the carrier substrate 9 . The remaining metallization 10 forms the inelastic contact surfaces for the front 14 and rear contact 15 . Separation columns 19 are also etched in this step for later separation.

The passivation layer 16 is applied in FIG. 2f. The trench between the front 14 and rear 15 contacts in the metallization 10 and the side surface of the radiation-emitting semiconductor structure 12 is passivated. Passivation is also carried out in a frame-like manner around the upper contacting layer 3 .

In FIG. 2g the metallization takes place for the production of the contacts 17 , 20 , to which the component, which will later be isolated, can be connected to a circuit. The entire metallic front side contact runs from the surface on which it is arranged in a finger shape 18 , along the passivation layer 16 to the carrier metallization 10 , where it forms the front side contact 20 on the front side contact surface 14 . The component can be electrically connected at the front contact 20 . The metallizations can be implemented using the lift-off method, among other things.

The final step in FIG. 2h is the separation of the radiation-emitting semiconductor components 21 . In this case, the carrier substrate 9 is severed at the gap 19 and thus the last connecting pieces from component 21 to component 21 are separated.

Fig. 3 shows the cross section through a radiation-emitting semiconductor component 21 having a thermally well-conductive support substrate 9. On the underside is the carrier substrate 9 , which has a higher thermal conductivity λ <1.1 W / K.cm compared to the GaP substrate. Ceramic, sapphire (Al ₂ O ₃ ) and silicon carbide (SiC) with values in the range from 2 W / K.cm to 4 W / K.cm are particularly suitable as materials for the carrier substrate 9 . In this exemplary embodiment, the carrier substrate 9 has a thickness of 100 μm and is metallized. This is followed by the adhesive layer 13 , which connects the carrier substrate and the radiation-emitting semiconductor structure 12 to one another. The metallization 11 is reflective, so that the light from the radiation-emitting semiconductor structure 12 is reflected back into the latter and is not lost there in the case of an absorbent carrier substrate 9 or adhesive. The carrier metallization 10 on the carrier substrate 9 is also divided into two partial areas. One forms the front side contact surface 14 and the other part forms the rear side contact surface 15 . The radiation-emitting semiconductor structure 12 is arranged on the rear side contact area. This consists of a window layer 8 made of p ++ GaP with a layer thickness in the range of approx. 3-6 µm. On this there is a 0.5 µm thick cladding layer 7 made of p + (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P. The layer on top is the actual photoactive layer 6 made of AlGaInP. There is a further approximately 0.5 µm thick cladding layer 5 made of n + (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P. A current distribution layer 4 made of highly doped n ++ (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P is arranged after this, which ensures a favorable current distribution and whose layer thickness is in the range of approximately 1-2 μm. At the very top is the highly doped, transparent contacting layer 3 , in particular n ++ Ga _0.75 In _0.25 P. The thickness of this contacting layer 3 is approximately 0.02 μm. The radiation-emitting semiconductor structure 12 is surrounded by a passivation layer 16 , which also surrounds the surface of the contacting layer 3 in a frame-like manner and is arranged in the trench between the front-side contact surface 14 and the rear-side contact surface 15 . On the remaining part of the back contact surface 15 of the carrier metallization 10 , a further metallization is applied, which then represents the back contact 17 of the component. The designation back contact 17 is chosen because it is connected to the underside of the radiation-emitting semiconductor structure 12 and not because it is located on the back of the entire component 21 . The front side contact 20 is also formed on the opposite side by a metallization. This metallization runs along the front contact surface 14 of the carrier metallization 10 on the side upwards along the passivation and then above the passivation layer finger-shaped 18 on the contact layer 3 of the semiconductor structure 12 .

FIG. 4 shows the top view of a radiation-emitting semiconductor component with a thermally highly conductive carrier substrate. The contacting layer 3 of the radiation-emitting semiconductor structure 12 is located here in the middle of the figure. The finger-shaped part 18 of the front-side contact 20 projects into this contacting layer. The finger-shaped arrangement serves to distribute the current density and increase the radiation yield. Opposite the front-side contact 20 is the rear-side contact 17 , which is not visible in this figure via the carrier metallization 10 to the rear side, that is to say the window layer 8 of the radiation-emitting semiconductor structure 12 . Front 20 and rear contact 17 serve as connections for the component 21 . This illustration also shows the passivation layer 16 , which is arranged between the contacts 17 , 20 and the radiation-emitting semiconductor structure 12 and which is arranged on the metallization 10 of the carrier substrate.

FIG. 5 shows a further application example analogous to FIG. 2b. The metallized semiconductor wafer bonded to the carrier substrate 9 is also shown here as a second step. However, in this application example, no conductive adhesive 13 , but an insulating one, such as silicone, was used. The top side 22 of the semiconductor structure is also not conductive, so that the electrical contact must be led out from an underlying layer 7 . For this reason, the surface of the uppermost layer 22 has notches 23 which extend to the closest layer 7 . The partial metallization 11 on the surface on the upper side 22 is attached in such a way that it fills and extends above the notches 23 . On the uppermost layer 22 , the insulating adhesive 13 is partially applied between the notches 23 , which together with the metallization 11 forms a plane. During the gluing process, the electrical contact to the carrier metallization 10 , which later forms the contact areas, and the adhesive connection 13 between the semiconductor structure and the carrier substrate 9 are formed. If the carrier substrate is absorbent, the carrier metallization should be reflective.

Not only plastic, glass, ceramic or a can also be used as the carrier substrate Semiconductors are used, but it could also be a metal use Find. Such a carrier substrate would then not have to be added be metallized in order to later form the contact areas.

Claims (6)

1. A method for producing radiation-emitting semiconductor wafers, in which several layers ( 2 , 3 , 4 , 5 , 6 , 7 , 8 ) are first epitaxized on a semiconductor substrate ( 1 ), on the uppermost epitaxial layer ( 8 ). a carrier substrate ( 9 ) is arranged and then the semiconductor substrate ( 1 ) is removed, characterized in that
before the uppermost layer ( 8 ) is connected to the carrier substrate ( 9 ), an at least partial metallization ( 11 ) is applied to the surface of the uppermost layer ( 8 ) and
this at least partially metallized top layer ( 8 ) is at least partially glued to the carrier substrate ( 9 ). 2. A method for producing radiation-emitting semiconductor wafers according to claim 1, characterized in that a reflective metallization ( 11 ) is applied to the surface of the uppermost layer ( 8 ). 3. A method for producing radiation-emitting semiconductor wafers according to claim 1 or 2, characterized in that a metallization ( 10 ) before the gluing with the uppermost layer ( 8 ) on the surface of the carrier substrate ( 9 ) facing the uppermost layer ( 8 ). is applied. 4. The method according to any one of claims 1 to 3, characterized in that a carrier substrate ( 9 ) is used, whose thermal conductivity is greater than that of GaP with 1.1 W / K.cm. 5. The method according to any one of claims 1 to 3, characterized in that a carrier substrate ( 9 ) made of silicon carbide, sapphire or ceramic is used. 6. Two-pole, radiation-emitting semiconductor component produced according to the method of claim 1, consisting of the carrier substrate ( 9 ) and a semiconductor structure ( 12 ), characterized in that on the metallization ( 10 , 11 ) between the carrier substrate and the semiconductor structure ( 12 ) at least a pole ( 17 , 20 ) is formed.