This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-63288, filed on Mar. 18, 2010; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a method for manufacturing a semiconductor light emitting device.
Manufacturing methods in which a semiconductor layer including a light emitting layer is separated from a growth substrate and transferred onto another substrate have been used for semiconductor light emitting devices such as light emitting diodes (LEDs). For example, JP-A 2005-303287 (Kokai) discusses increasing the productivity of a Group III nitride semiconductor light emitting device by separating a Group III nitride semiconductor layer from a growth substrate.
However, there are cases in which breakage and cracks of the substrate occur when the semiconductor layer is transferred onto the different substrate. Therefore, there is a need for a manufacturing method that can prevent breakage and cracks of the substrate.
In one embodiment, a method for manufacturing a semiconductor light emitting device characterized by bonding a first stacked body to a second stacked body is disclosed. The first stacked body includes a first substrate, a semiconductor layer, and a first metal layer. The second stacked body includes a second substrate and a second metal layer. The method can include overlaying the first metal layer and the second metal layer by shifting a cleavage direction of the first stacked body from a cleavage direction of the second stacked body and by bringing the first metal layer and the second metal layer into contact. The method can include bonding the first stacked body and the second stacked body by increasing a temperature in a state of pressing the first stacked body and the second stacked body into contact.
Embodiments of the invention will now be described with reference to the drawings. In the embodiments hereinbelow, similar portions in the drawings are marked with like numerals and a detailed description thereof is omitted as appropriate; and different portions are described as appropriate.
A method for manufacturing a semiconductor light emitting device according to one embodiment of the invention includes a process of overlaying a first stacked body including a first metal layer provided on a first substrate with a second stacked body including a second metal layer provided on a second substrate by shifting a cleavage direction of the first substrate from a cleavage direction of the second substrate and by bringing the first metal layer and the second metal layer into contact. The first stacked body includes a semiconductor layer on the first substrate, where the semiconductor layer includes a light emitting layer that radiates light; and the first metal layer is provided on the semiconductor layer.
The method further includes a process of bonding the first stacked body and the second stacked body by increasing a temperature in a state of pressing the first stacked body and the second stacked body into contact.
As illustrated in
On the other hand, as illustrated in
In the case where a light emitting layer 13 included in the semiconductor layer 12 is an InGaAlP semiconductor, the semiconductor light emitting device can emit visible light in a wavelength range of yellowish-green to red. A good crystal can be provided easily because the semiconductor layer 12 is made of an InGaAlP compound crystal and has lattice matching with GaAs.
Then, as illustrated in
For example, the cleavage direction of the first stacked body 20 matches the cleavage direction of the n-type GaAs substrate 10; and the cleavage direction of the second stacked body 40 matches the cleavage direction of the p-type Si substrate 30. Accordingly, in the case where a major surface 25 of the n-type GaAs substrate 10 is a (100) surface and a major surface 45 of the p-type Si substrate 30 is a (100) surface, the first stacked body 20 and the second stacked body 40 are bonded with the <110> direction of the n-type GaAs substrate 10 shifted from the <110> direction of the p-type Si substrate 30.
The first metal layer 15 or the second metal layer 35 may include, for example, gold (Au) and metals including Au such as AuIn, AuSn, etc. The bonding strength between Au and Au may be increased by the first metal layer 15 and the second metal layer 35 having a multilayered structure of Ti/Pt/Au. A solder alloy of InSn and the like also may be used. The first metal layer 15 or the second metal layer 35 may include tungsten (W) as a barrier metal. The first metal layer and the second metal layer also may be, for example, copper (Cu) or aluminum (Al).
An example of the substrate bonding process will now be described with reference to
In the substrate bonding process according to this embodiment, for example, the first stacked body 20 and the second stacked body 40 are heated and bonded after being overlaid in a vacuum.
First, the first stacked body 20 and the second stacked body 40 are placed in the interior of a not-illustrated vacuum container; and the interior of the vacuum container is brought to a low-pressure state.
Then, for example, surface activation may be performed prior to overlaying the first stacked body 20 and the second stacked body 40. (Surface activation A)
Specifically, unnecessary oxide films, organic substances, and the like are removed from the surface of the first metal layer and the surface of the second metal layer 35 by, for example, irradiating an argon (Ar) ion beam. Also, the surface of the first metal layer 15 and the surface of the second metal layer 35 may be exposed to a plasma atmosphere.
Also, the first stacked body 20 and the second stacked body 40 may be overlaid without performing the surface activation.
Continuing, the surface of the first metal layer 15 and the surface of the second metal layer 35 are brought into contact; and the first stacked body 20 and the second stacked body 40 are overlaid. (Alignment B)
Specifically, the surface of the first metal layer 15 and the surface of the second metal layer 35 are disposed opposing each other; and the cleavage directions of the n-type GaAs substrate 10 and the p-type Si substrate 30 are matched. Further, either of the substrates is rotated to shift the angle between the cleavage directions thereof to a prescribed angle. Then, the first metal layer 15 and the second metal layer 35 are brought into contact to overlay the first stacked body 20 and the second stacked body 40.
Then, a pressing load is applied between the first stacked body 20 and the second stacked body 40 to closely adhere the first stacked body 20 and the second stacked body 40 to each other. (Close adhesion C)
It is desirable for the temperature at which the first stacked body 20 and the second stacked body 40 are closely adhered to be not more than 100° C. Thereby, it is possible to reduce the warp occurring due to differences in the coefficient of thermal expansion between the n-type GaAs substrate 10 and the p-type Si substrate 30, for example, when returning the bonded substrates to room temperature.
The load applied between the first stacked body 20 and the second stacked body 40 may be not less than 10 kg/cm2 and not more than 30 kg/cm2. It is desirable to apply, for example, a pressing load not less than 10 kg/cm2 to provide a state in which the surface of the first metal layer 15 and the surface of the second metal layer 35 are entirely and closely adhered. Further, it is desirable for the load to be not more than 30 kg/cm2 so that breakage and cracks of the first stacked body 20 and the second stacked body 40 do not occur.
The maximum load of, for example, about 20 kg/cm2 can be applied between the n-type GaAs substrate 10 and the p-type Si substrate 30 when overlaid with matched cleavage directions. On the other hand, it is possible to apply a pressing load of up to 30 kg/cm2 by overlaying with a shifted angle between the two cleavage directions of not less than 1°.
Continuing, the first stacked body 20 and the second stacked body 40 are heated in the overlaid state while the load is applied; and the temperature is increased to a prescribed temperature (C to D).
For example, in the case where the first metal layer 15 and the second metal layer 35 are metals including Au, the first metal layer 15 and the second metal layer 35 are heated to a temperature not less than 250° C. This is because it is desirable to increase the temperature to not less than 250° C. to bond the first stacked body 20 and the second stacked body 40 such that defects such as voids and the like do not occur between the first metal layer 15 and the second metal layer 35.
On the other hand, it is desirable to maintain the temperature at not more than 350° C. so that breakage and cracks do not occur in the first stacked body 20 and the second stacked body 40 due to stress caused by differences in the coefficient of thermal expansion between the n-type GaAs substrate 10 and the p-type Si substrate 30.
Continuing, after maintaining the first stacked body 20 and the second stacked body 40 in the overlaid state for a constant time at the prescribed temperature, the first stacked body 20 and the second stacked body 40 are cooled to a temperature of 100° C. or less and removed from the vacuum container. (D to E to removal F)
During this interval, the overlaid first stacked body 20 and second stacked body 40 are maintained in the state of the applied prescribed load until the temperature is reduced to 100° C. or less.
By irradiating, for example, the surface of the first metal layer 15 and the surface of the second metal layer 35 with an Ar ion beam in the substrate bonding process recited above, active bonds of the atoms can be exposed in the metal surface. Thereby, it is possible to reduce the energy necessary to bond the metal atoms of the surface of the first metal layer 15 to the surface of the second metal layer 35. In other words, the bonding is possible at a lower temperature than in the case where the Ar ion beam is not irradiated. For example, there are cases where bonding of the substrates is possible at room temperature when the bonding process is performed in an ultra-high vacuum state after the surface activation.
Continuing as illustrated in
Then, the semiconductor light emitting device is completed by forming an n-electrode on a front face 48 of the semiconductor layer 12 from which the n-type GaAs substrate 10 is removed and by forming a p-electrode on a back face 49 of the p-type Si substrate 30.
As another embodiment, the first substrate may be a sapphire substrate; and the semiconductor layer may be formed using a nitride semiconductor. For example, the first stacked body including a semiconductor layer, in which an n-type GaN layer/light emitting layer/p-type GaN layer are stacked, may be provided by MOCVD on the sapphire substrate. The light emitting layer may include a MQW (Multi-Quantum Well) layer in which an InxGa1-xN layer (0≦x≦1) and an AlyGa1-yN layer (0≦y<1) are alternately stacked.
In the process of removing the first substrate illustrated in
Operations and effects of the method for manufacturing the semiconductor light emitting device according to this embodiment will now be described with reference to
In the manufacturing method according to the comparative example illustrated in
The property recited above is advantageous when subdividing the semiconductor devices constructed using the bonded substrate 50 into individual chips. For example, in the case where the first stacked body 20 is formed using a GaAs (100) substrate and the second stacked body 40 is formed using a Si (100) substrate, the cleavage direction of both is the <110> direction; and the (011) surface and the (101) surface have cleaving properties. Accordingly, the bonded substrate 50 bonded with the two matched cleavage directions has the advantage that rectangular semiconductor device chips can be cut out easily because the bonded substrate 50 has orthogonal cleaving surfaces of the (011) surface and the (101) surface. Therefore, when bonding two substrates, manufacturing methods are often used, where the two cleavage directions match each other.
However, matching the cleavage directions of two substrates to have a common cleaving surface means that the bonded substrates are easily broken. Specifically, in the substrate bonding process described above, there is a high possibility that both the first stacked body 20 and the second stacked body 40 may break due to stress occurring between the first stacked body 20 and the second stacked body 40 due to heating, locally concentrated stress due to protrusions and the like existing at the bonding interface 47, etc.
Conversely, in the manufacturing method according to this embodiment as illustrated in
Thereby, it is possible to suppress the breakage and cracks occurring in the substrate bonding; and the manufacturing yields can be increased. Specifically, it is desirable for the shift between the cleavage direction 20H of the first stacked body 20 and the cleavage direction 40H of the second stacked body 40 to be not less than 1°.
For example, the p-type Si substrate 30 of the second stacked body 40 is stronger than the n-type GaAs substrate 10 of the first stacked body 20; and the first stacked body 20 breaks more easily than the second stacked body 40. Accordingly, in the bonded substrate 60 as illustrated in
In a semiconductor substrate 40b illustrated in
Continuing as illustrated in
In the case where a shifted angle θ is large between the cleavage direction 40H of the p-type Si substrate 30 and the cleavage direction 20H of the semiconductor layer 12, there are cases where chipping 67a and 67b such as that illustrated in
As described above, it is desirable for the shifted angle θ of the cleavage direction to be not less than 1° to increase the strength of the bonded substrates. Accordingly, it is desirable for the shifted angle θ between the cleavage direction of the first stacked body 20 and the cleavage direction of the second stacked body 40 to be not less than 1° and not more than 10° in the state in which the first stacked body 20 and the second stacked body 40 are overlaid.
The method for manufacturing the semiconductor light emitting device according to this embodiment further includes: a process of separating the first substrate while leaving the semiconductor layer on the second stacked body; a process of providing a dicing groove along the cleavage direction of the second stacked body to separate the semiconductor layer into individual semiconductor devices; and a process of cutting the second stacked body along the dicing groove.
Similarly to the semiconductor substrate 40b described above, the semiconductor layer 12 is transferred onto the second stacked body 40 in a semiconductor substrate 40c illustrated in
The dicing groove 72 can be made by, for example, RIE (Reactive Ion Etching) using an etching gas including chlorine (Cl2) or fluorine (F). Wet etching also can be used.
By the manufacturing method according to this embodiment, the individual light emitting devices 75 can be subdivided along the dicing groove 72 into chips. At this time, the cutting is easy because the dicing groove 72 and the cleavage direction 40H are matched to each other. Moreover, because the semiconductor layer 12 is separated by the dicing groove 72, there is no contact with the dicing blade when subdividing and, for example, the chipping 67a and 67b does not occur.
In other words, according to this embodiment, the shifted angle θ between the cleavage direction 20H of the first stacked body 20 and the cleavage direction 40H of the second stacked body 40 can be greater than 10°. Thereby, the strength of the bonded substrate 60 can be increased further.
In this embodiment as well, the first metal layer or the second metal layer may include, for example, Au or Au alloy. The first stacked body and the second stacked body are overlaid at a temperature not more than 100° C. The substrate bonding process heats the first stacked body and the second stacked body to a temperature range of not less than 250° C. and not more than 350° C. and further includes a cooling process; and the pressing load applied between the first stacked body and the second stacked body can be not less than 10 kg/cm2 and not more than 30 kg/cm2.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.
Number | Date | Country | Kind |
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2010-063288 | Mar 2010 | JP | national |