Bonding type semiconductor substrate, semiconductor light...

Details Bonding type semiconductor substrate, semiconductor light... Bonding type semiconductor substrate, semiconductor light...

2000-06-08

2002-10-15

Jackson, Jr., Jerome (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

Incoherent light emitter structure

With heterojunction

C257S094000, C257S095000, C257S096000, C257S097000

Reexamination Certificate

active

06465809

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a bonding type semiconductor substrate and a semiconductor light emitting element, and preparation processes thereof. Particularly, the present invention relates to a bonding type semiconductor substrate based on a novel wafer direct bonding technique, a light emitting element such as LEDs (light emitting diode) with a high brightness obtained by applying the technique, and preparation processes thereof.
A light emitting element based on a conventional technique will be explained with reference to drawings attached hereto.
FIG. 22
shows an embodiment of a visible light LED of InGaAlP based on a conventional technique.
In an LED
100
shown in
FIG. 22
, InGaAlP epitaxial growth layers
84
,
85
,
86
contributing to light emission are formed on an n-type GaAs substrate
82
. Although not shown in this drawing, a buffer layer may be disposed between the substrate and the epitaxial growth layer in compliance with required specifications in order to obtain an excellent light emitting layer.
Electrodes
89
for supplying an electric current are each disposed on the upper surface of the epitaxial growth layer
86
and the lower surface of the substrate
82
, respectively. Although not shown in the same drawing, a layer for diffusing the electric current or a layer for taking an electric contact is often disposed between an upper electrode
89
and the epitaxial growth layer
86
. Among the epitaxial growth layers
84
,
85
,
86
, the layer which can emit light by the recombination of carriers is the active layer
85
. The epitaxial layers
84
and
85
formed on and under the active layer
85
are the cladding layers
84
and
86
having a wider band gap than the active layer in order to confine the carriers and to thereby heighten an emission efficiency.
For these epitaxial growth layers
84
,
85
and
86
, the band gap is required to be optimized according to a design for the purpose of adjusting the wavelength of the emission and for the purpose of confining the carriers. Furthermore, it is desirable for a good epitaxial growth that a lattice constant of the epitaxial growth layer matches a lattice constant of the substrate
82
. Since InGaAlP which is a group III-V compound contains three elements of In, Ga and Al as components in the group III, the band gap and the lattice constant can be independently designed by selecting a composition ratio of these elements.
For example, when a composition of the epitaxial growth layer is represented by the following formula
In
x
(Ga
1−y
Al
y)
1−x
P  (1),
the lattice constant of the epitaxial growth layer almost matches that of a GaAs substrate by setting a composition ratio (x) of In to 0.5. The band gap can be controlled by adjusting a composition ratio (y) between Al and Ga, while x=0.5 is kept up.
For example, in order to obtain a red light emitting LED having a wavelength of 644 nm, the composition ratio of the active layer
85
is set to x=0.5 and y=0.043, and the composition ratio of the cladding layers
84
,
86
is set to x=0.5 and y=0.7. Moreover, in order to obtain a green light emitting LED having a wavelength of 562 nm, the composition ratio of the active layer
85
is set to x=0.5 and y=0.454, and the composition ratio of the cladding layers
84
,
86
is set to x=0.5 and y=1.00, i.e., InAlP.
As illustrated in the above, for InGaAlP epitaxial growth layers, the wavelength of the emission can be selected within a region of visible light. Furthermore, since the layers can epitaxially grow under the lattice matching condition with a GaAs substrate which is most general as a compound semiconductor substrate, there exist advantages that the substrate is easily available and the epitaxial growth is relatively easy.
On the contrary, a GaAs substrate has a disadvantage that it absorbs light in a region of visible light. Therefore, part of the light emitted on an InGaAlP epitaxial growth layer is absorbed by GaAs substrate, and hence a brightness of LED decreases unavoidably. For avoiding the decrease of the brightness, a material which is transparent in the region of the visible light is preferably employed as a substrate. The usual transparent material is GaP, but since the GaP substrate cannot obtain the lattice matching with InGaAlP, the good epitaxial growth is difficult. In order to solve this problem, U.S. Pat. No. filed 5,376,580 in 1993 proposes a method for a wafer bonding between an InGaAlP epitaxial growth layer and a GaP substrate. This proposed method comprises removing a GaAs substrate from the epitaxial growth layer, closely bonding a GaP substrate instead of the GaAs substrate, and then carrying out a heat treatment under pressure to integrally bond them. According to this method, the increase of the brightness of LED can be attained. However, the stability and productivity of the wafer bonding step are insufficient, because the epitaxial growth layer after the removal of the GaAs substrate is thin and thus its handling is difficult, and a special apparatus is necessary for the heat treatment under pressure.
Next, the following explains the wafer bonding. If two different kinds of wafers can be integrally bonded, a laminated structure comprising different materials could be obtained regardless of the lattice constant, and a different substance can be buried inside as represented by SOI (silicon on insulator). For these reasons, various wafer bonding techniques have been proposed hitherto. For example, the above-mentioned bonding method of subjecting two wafers to the heat treatment while they are pressed is disclosed in Japanese Patent No. 765892 filed in 1970. The wafer bonding technique has been desired for a long time, but it is difficult to accomplish the integral bonding all over the surface of the wafer, so that this technique has not been practiced.
The present inventors have developed a technique called “direct bonding” or “direct joining” as a practicable technique. For example, Japanese Patent No. 1420109 filed in 1983 and the like describes the direct bonding between Si wafers, and Japanese Patent No. 2040637 filed in 1985 and the like describes the direct bonding between compound semiconductor wafers.
The direct bonding technique comprises mutually closely bonding two substrates having mirror-polished surfaces by themselves at room temperature under a substantially dust-free atmosphere, and then integrally joining them by a heat treatment. This technique has an advantage that the whole surface can be joined without leaving any unbonded part, because the whole surfaces are closely bonded to each other prior to the heat treatment. Moreover, it is not necessary to apply a pressure during the heat treatment, any special apparatus or equipment is not required. The mechanism of the direct bonding between the Si wafers is understood as follows.
Namely, at the beginning, OH groups are formed on the surface of the wafer by cleaning or washing with water. Then, when the surfaces of the two wafers are contacted with each other, the OH groups attract each other by a hydrogen bond, so that the wafers closely bond at room temperature. A bonding power in this case is strong enough to eliminate a usual warp of the wafer, whereby the close bonding all over the surfaces can be achieved. During the heat treatment, a dehydrative condensation (Si—OH:HO—Si→Si—O—Si+H
2
O) occurs at a temperature higher than 100° C., and the wafers bond to each other via oxygen atoms, thereby increasing a bonding strength. When the temperature further rises, the diffusion and rearrangement of the atoms in the vicinity of a bonding interface occur, so that the wafers are integrated mechanically and electrically. The bonding mechanism of the compound semiconductors is considered to be similar.
Next, one example of a preparation process of an LED comprising an InGaAlP-based epitaxial growth layer closely bonded to the GaP substrate by utilizing the direct bonding will be explained with refe

Affiliated with

Also associated with

Rating

Bonding type semiconductor substrate, semiconductor light... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Bonding type semiconductor substrate, semiconductor light..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bonding type semiconductor substrate, semiconductor light... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2972417