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Method for manufacturing light emitting device

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Title: Method for manufacturing light emitting device.
Abstract: A method for manufacturing a light emitting device, includes: forming a first multilayer body including a first substrate, a first semiconductor layer provided on the first substrate and having a light emitting layer, and a first metal layer provided on the first semiconductor layer; forming a second multilayer body including a second substrate having a thermal expansion coefficient different from a thermal expansion coefficient of the first substrate, and a second metal layer provided on the second substrate; a first bonding step configured to heat the first metal layer and the second metal layer being in contact with each other; removing the first substrate after the first bonding step; and a second bonding step configured to perform, after the removing, heating at a temperature higher than a temperature of the first bonding step. ...


Browse recent Kabushiki Kaisha Toshiba patents - Tokyo, JP
Inventors: Yasuhiko Akaike, Ryo Saeki, Yoshinori Natsume
USPTO Applicaton #: #20120104446 - Class: 257 98 (USPTO) - 05/03/12 - Class 257 
Active Solid-state Devices (e.g., Transistors, Solid-state Diodes) > Incoherent Light Emitter Structure >With Reflector, Opaque Mask, Or Optical Element (e.g., Lens, Optical Fiber, Index Of Refraction Matching Layer, Luminescent Material Layer, Filter) Integral With Device Or Device Enclosure Or Package

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The Patent Description & Claims data below is from USPTO Patent Application 20120104446, Method for manufacturing light emitting device.

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CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of application Ser. No. 12/544,353 filed Aug. 20, 2009; the entire contents of which are incorporated herein by reference.

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-028908, filed on Feb. 10, 2009; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for manufacturing a light emitting device.

2. Background Art

Semiconductor light emitting devices capable of emitting visible light including blue to red light can be widely used in such applications as illumination lamps, displays, and traffic signals. Such light emitting devices with high brightness can find wider application in light sources replacing fluorescent lamps and incandescent bulbs. Furthermore, reduction of operating current facilitates achieving low power consumption.

Here, in a light emitting device which uses a substrate made of e.g. GaAs having a bandgap wavelength of generally 870 nm, visible light emitted from the light emitting device and having emission wavelengths of 700 nm or less is absorbed by the substrate, causing the problem of decreased brightness.

If the substrate is made of e.g. GaP having a bandgap wavelength of generally 550 nm, optical absorption by the substrate can be reduced for visible light having longer wavelengths, which facilitates increasing the brightness. However, the lattice constant of InGaAlP-based semiconductors capable of emitting visible light in the wavelength range from yellow-green to red differs from the lattice constant of GaP by as large as several %, which makes it difficult to directly form an InGaAlP-based light emitting layer with low crystal defect density on a GaP substrate.

JP-A 2005-019424 (Kokai) discloses a technique related to a method for manufacturing a light emitting device by wafer bonding. In this technique, a substrate and a light emitting layer section are bonded via a metal layer. Here, a diffusion blocking semiconductor layer is provided to prevent metal diffusion from the metal layer into the light emitting layer, thereby preventing decrease in light emission characteristics.

However, it is difficult to achieve good wafer bonding characteristics while preventing cracking of the substrate in the heat treatment step for substrate lamination.

SUMMARY

OF THE INVENTION

According to an aspect of the invention, there is provided a method for manufacturing a light emitting device, including: forming a first multilayer body including a first substrate, a first semiconductor layer provided on the first substrate and having a light emitting layer, and a first metal layer provided on the first semiconductor layer; forming a second multilayer body including a second substrate having a thermal expansion coefficient different from a thermal expansion coefficient of the first substrate, and a second metal layer provided on the second substrate; a first bonding step configured to heat the first metal layer and the second metal layer being in contact with each other; removing the first substrate after the first bonding step; and a second bonding step configured to perform, after the removing, heating at a temperature higher than a temperature of the first bonding step.

According to an aspect of the invention, there is provided a method for manufacturing a light emitting device, including: forming a first multilayer body including a first substrate made of one of GaAs, GaP, and SiC, a first semiconductor layer provided on the first substrate and having a light emitting layer, and a first metal layer provided on the first semiconductor layer; forming a second multilayer body including a second substrate having a thermal expansion coefficient different from a thermal expansion coefficient of the first substrate and made of one of Si, Ge, and SiC, and a second metal layer provided on the second substrate; a first bonding step configured to heat the first metal layer and the second metal layer being in contact with each other; removing the first substrate after the first bonding step; and a second bonding step configured to perform, after the removing, heating at a temperature higher than a temperature of the first bonding step.

According to an aspect of the invention, there is provided a method for manufacturing a light emitting device, including: forming a first multilayer body including a first substrate made of sapphire, a first semiconductor layer provided on the first substrate and having a light emitting layer, and a first metal layer provided on the first semiconductor layer; forming a second multilayer body including a second substrate having a thermal expansion coefficient different from a thermal expansion coefficient of the first substrate and made of one of Si, Ge, and SiC, and a second metal layer provided on the second substrate; a first bonding step configured to heat the first metal layer and the second metal layer being in contact with each other; removing the first substrate after the first bonding step; and a second bonding step configured to perform, after the removing, heating at a temperature higher than a temperature of the first bonding step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a light emitting device according to a first embodiment;

FIGS. 2A to 2D are process cross-sectional views of a method for manufacturing the light emitting device according to the first embodiment;

FIGS. 3A to 3D are process cross-sectional views of a method for manufacturing a light emitting device according to a comparative example;

FIGS. 4A to 4D are process cross-sectional views showing a method for manufacturing a light emitting device according to a second embodiment

FIGS. 5A to 5D are process cross-sectional views of a light emitting device according to a variation of the second embodiment;

FIG. 6 is a schematic cross-sectional view of a light emitting device according to a third embodiment;

FIGS. 7A to 7D are process cross-sectional views showing a method for manufacturing the light emitting device of the third embodiment; and

FIG. 8 is a schematic cross-sectional view showing a light emitting device according to a variation of the third embodiment.

DETAILED DESCRIPTION

OF THE INVENTION

Embodiments of the invention will now be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a light emitting device according to a first embodiment of the invention.

A second substrate 40 is illustratively made of p-type Si and has a thickness of e.g. 250 μm. However, the substrate is not limited thereto, but can be made of other materials such as Ge and SiC, and the conductivity type can be n-type. The second substrate 40 and a second metal layer 42 provided thereon constitute a second multilayer body 43.

A semiconductor layer 46 made of a compound semiconductor is bonded to the second multilayer body 43 via a first metal layer 44. That is, the first metal layer 44 and the second metal layer 42 are bonded at a bonding interface 47. Here, the first metal layer 44 and the second metal layer 42 can be illustratively made of Ti, Pt, and Au stacked in this order. In this case, the uppermost Au films are bonded to each other.

An upper electrode 50 is provided on the semiconductor layer 46, and a lower electrode 52 is provided on the second substrate 40. The semiconductor layer 46 includes a light emitting layer 46a, from which light is emitted upward and laterally. Light emitted downward from the light emitting layer 46a can be reflected upward or laterally by the first metal layer 44, which serves to increase the brightness. If the light emitting layer 46a is made of InGaAlP-based semiconductors, the emitted light can be in the wavelength range of visible light.

In this specification, the InGaAlP-based semiconductor refers to a material represented by a composition formula Inx(GayAl1−y)1−xP (where 0≦x≦1, 0≦y≦1), and also includes those doped with p-type or n-type impurities.

FIGS. 2A to 2D are process cross-sectional views of a method for manufacturing the light emitting device according to the first embodiment.

As shown in FIG. 2A, on a first substrate 48 illustratively made of n-type GaAs, a semiconductor layer 46 including InGaAlP or the like is formed by MOCVD (metal organic chemical vapor deposition) method or MBE (molecular beam epitaxy) method, for instance, and a first metal layer 44 is further formed to construct a first multilayer body 49. If the light emitting layer 46a is made of InGaAlP-based semiconductors, it can emit visible light in the wavelength range from yellow-green to red. Thus, the semiconductor layer 46 illustratively made of InGaAlP is readily lattice-matched with GaAs, and hence can be formed as a good crystal. In contrast, it is difficult to directly form an InGaAlP semiconductor layer on a Si substrate, which has a different lattice constant.

The source material used in the MOCVD method can illustratively be a metal-organic compound such as TMG (trimethylgallium), TMA (trimethylaluminum), and TMI (trimethylindium), or a hydride gas such as arsine (AsH3) and phosphine (PH3). A p-type impurity can illustratively be Zn derived from DMZ (dimethylzinc), and an n-type impurity can illustratively be Si.

On the other hand, as shown in FIG. 2B, on the second substrate 40 illustratively made of p-type Si, a second metal layer 42 is formed by vacuum evaporation method or the like to construct a second multilayer body 43.

Next, as a first bonding step, the first metal layer 44 and the second metal layer 42 are brought into contact at room temperature, for instance, and heated for generally 30 minutes in the temperature range of 100-200° C., for instance. Thus, as shown in FIG. 2C, the first multilayer body 49 and the second multilayer body 43 are bonded at the bonding interface 47.

Here, the lamination is preferably performed in a vacuum or under low pressure, for instance, because air and the like at the lamination interface can be excluded to achieve closer contact. Furthermore, heating in an inert gas atmosphere or vacuum is more preferable because oxidation of the first and second metal layers 44, 42 can be prevented.

Subsequently, as shown in FIG. 2D, the first substrate 48 is removed by at least one of mechanical polishing method and we etching method. Here, the first substrate 48 can be completely removed or partly left. Subsequently, as a second bonding step, heating is performed for generally 30 minutes in the temperature range of 300-500° C., for instance, which is higher than the temperature of the first bonding step. The second bonding step is preferably performed in an inert gas atmosphere because oxidation of the first and second metal layer 44, 42 can be prevented. More preferably, the first and second metal layers 44, 42 have a multilayer structure of Ti/Pt/Au, and the first and second bonding steps are performed under a load, because the Au-Au bonding strength can be increased.

Subsequently, an upper electrode 50 and a lower electrode 52 are formed, and ohmic contact is formed between the upper electrode 50 and the semiconductor layer 46, and between the lower electrode 52 and the second substrate 40. Here, the sintering temperature for forming ohmic contact is 350° C., for instance, which is lower than the temperature of the second bonding step. In this case, a stable ohmic contact can be formed between the upper electrode 50 and the semiconductor layer 46, and between the lower electrode 52 and the second substrate 40.

Alternatively, after the process of removing the first substrate 48, an upper electrode 50 and a lower electrode 52 are formed, and a second bonding step for heating to a temperature higher than the temperature of the first bonding step can be performed. In this case, if the temperature of the second bonding step is in the range of 350-500° C., for instance, ohmic contact can be formed while increasing the bonding strength. Thus, the light emitting device shown in FIG. 1 is completed.

Furthermore, in the first bonding step, if the Au or other metal surface to be bonded is irradiated with ions, plasma and the like, unwanted oxide film, organic matter and the like can be removed, and active bonds of atoms can be exposed to the metal surface. That is, the energy required for coupling can be reduced. This is more preferable because it facilitates bonding at a lower temperature. Bonding under an ultrahigh vacuum after the surface activation may allow the wafer to be bonded at a temperature near normal temperature.

In this manufacturing method, the first bonding step is performed at a lower temperature than the second bonding step. Here, it is easy to ensure bonding strength enough to avoid delamination of the semiconductor layer 46, which is an epitaxial layer, in the process of removing the first substrate 48. Furthermore, the second bonding step is performed after the first substrate 48 is removed. The absence of the second bonding step may result in failing to ensure bonding strength enough to withstand the chip separation process. In this embodiment, the second bonding step performed at a higher temperature than the temperature of the first bonding step further increases the bonding strength between the first metal layer 44 and the second metal layer 42, and can prevent chip breakage during the chip separation and assembly process.

Furthermore, wafer cracks, dislocations and the like are reduced at the bonding interface 47, which facilitates achieving device characteristics with improved brightness and reliability. Here, a higher temperature is required to bond a semiconductor layer to a substrate made of a semiconductor, sapphire or the like without the intermediary of a metal layer.

If the second substrate 40 is made of Si, the assembly process can achieve high mass productivity because the substrate has higher strength than that made of GaAs and the like and facilitates chip separation.

FIGS. 3A to 3D are process cross-sectional views of a method for manufacturing a light emitting device according to a comparative example.

As shown in FIG. 3A, on a first substrate 148 illustratively made of n-type GaAs, a semiconductor layer 146 illustratively made of InGaAlP-based compound semiconductors and a first metal layer 144 are formed by vacuum evaporation method or the like. The first metal layer 144 can be illustratively made of Ti, Pt, and Au stacked in this order from the semiconductor layer 146 side.

On the other hand, as shown in FIG. 3B, on a second substrate 140 illustratively made of p-type Si, a second metal layer 142 illustratively made of Ti/Pt/Au is formed by vacuum evaporation method or the like.

Next, as a bonding step, the first and second metal layers 144, 142 at the surface of these wafers are laminated in a vacuum, for instance, and heated for generally 30 minutes in the temperature range of 300-500° C. in an inert gas atmosphere, for instance. Thus, the two wafers are bonded at a bonding interface 147 (FIG. 3C).

Subsequently, as shown in FIG. 3D, the first substrate 148 is removed by at least one of mechanical polishing and we etching. Here, the first substrate 148 can be completely removed or partly left. Subsequently, an upper electrode and a lower electrode are formed, and separation into chips is performed.



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stats Patent Info
Application #
US 20120104446 A1
Publish Date
05/03/2012
Document #
13343810
File Date
01/05/2012
USPTO Class
257 98
Other USPTO Classes
257103, 257E33066
International Class
01L33/60
Drawings
9



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