Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
1999-09-07
2001-06-19
Pham, Long (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
C438S022000, C438S047000, C438S906000, C438S909000
Reexamination Certificate
active
06248607
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for manufacturing semiconductor light emitting device such as light emitting diode or semiconductor laser employing gallium nitride based compound semiconductor for generating light of blue type (blue to yellow) having a high luminance. More particularly, the present invention relates to a method for manufacturing semiconductor light emitting device wherein annealing treatment for activating a p-type layer can be performed in a short time to achieve sufficient activation thereof.
BACKGROUND OF THE INVENTION
Semiconductor light emitting chips (hereinafter referred to as “LED chips”) generating blue type light are conventionally manufactured in the following manner. As shown in
FIG. 2
, there are sequentially formed, through epitaxial growth onto a sapphire substrate
21
, an n-type layer (cladding layer)
23
of e.g. n-type GaN, an active layer (light emitting layer)
24
of e.g. InGaN based compound semiconductor (wherein the ratio of In and Ga may be varied as it similarly applies hereinafter) which is a material which band gap energy is smaller than that of the cladding layer and which determines the light
25
emitting wavelength, and a p-type layer (cladding layer) of p-type GaN. Annealing treatment for activating a p-type layer can be performed i atmosphere of vacuum condition, nitrogen gas, inert gas, or the like. A p-side electrode
28
is formed onto a surface of the substrate with a current diffusion layer
27
interposed between, and a part of the laminated semiconductor layers are etched so that an n-side electrode
29
is formed on the exposed surface of the n-type layer
23
. Thereafter, by dividing the wafer into individual chips, LED chips as shown in
FIG. 2
can be obtained.
As mentioned above, in conventional methods of manufacturing semiconductor light emitting device employing gallium nitride based compound semiconductor, annealing treatment is performed after laminating the semiconductor layers in order to activate the p-type layer. This annealing is performed, as mentioned, in a vacuum condition or in an inert gas atmosphere. Such treatment is taken because surfaces of gallium nitride based compound semiconductors are slightly oxidized in case of undergoing heat treatment at approximately 600° C. at an oxygen atmosphere though it presents stability against corrosion, so that adhesion with a current diffusion layer that is to be formed thereon or electrical characteristics such as electrical conductivity are degraded.
However, it is conventionally required to perform annealing treatment at high temperature ranging from 500 to 800° C. and for a long time of approximately 1 to 2 hours otherwise no sufficient activation can be achieved and the electrical resistance of the p-type layer can not be sufficiently decreased.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for manufacturing semiconductor light emitting device, wherein heat treatment for activation of the p-type layer of semiconductor light emitting device laminated with gallium nitride based compound semiconductor can be performed in a short time to reliably perform activation.
In repeatedly carrying out investigations on how to perform heat treatment for activation of the p-type layer in a short time, the inventor has found that the reason why the p-type layer is not sufficiently activated and the electric resistance not decreased in the absence of heat treatment is that H of carrier gas H
2
or reactive gas NH
3
that is used at the time of laminating the semiconductor layers is bound to Mg used as a dopant for the p-type layer so that Mg does not function as a dopant but provides high resistance. Thus, the inventor has found out that activation treatment can be performed in a short time by performing heat treatment at an atmosphere in which H (hydrogen atom) can be easily drawn out.
In a method of manufacturing semiconductor light emitting device according to the present invention, when a gallium nitride based compound semiconductor layers which includes at least an n-type layer and p-type layer which forms a light emitting layer, are laminated on a substrate and heat treatment is performed for activation of the p-type layer of the laminated semiconductor layers, the heat treatment is performed at an atmosphere including oxygen.
Here, an atmosphere including oxygen indicates an atmosphere having an oxygen content ranging from several tenths % up to 100% expressed in volume ratios, that is, an atmosphere including a minute amount of oxygen within inert gas up to an atmosphere of oxygen only, and the oxygen is not limited to be directly contained by may be oxidized gas such as ozone or N
2
O. Further, a gallium nitride based compound semiconductor refers to a semiconductor comprising a compound having Ga of III group elements and N of V group elements, wherein one part or all of Ga of III group elements may be substituted by other III group elements such as Al or In and/or a part of N of the V group elements may be substituted by other V group elements such as P or As.
By employing this method, oxygen residing in the periphery of the laminated semiconductor layer draws H that has combined with Mg within the p-type layer since oxygen is easily combined with hydrogen so that H and O are compound. Consequently, H that is hardly drawn upon combining within the p-type layer can be easily drawn so that Mg is in a free condition and ready to sufficiently function as a dopant. Thus, activation treatment can be performed in a short time.
More particularly, the method of the present invention comprises the steps of (a) sequentially laminating on a substrate a buffer layer, an n-type layer, an activation layer and a p-type layer of gallium nitride based compound semiconductor, (b) performing activation treatment by putting the substrate laminated with semiconductor layers into a heating furnace for activating the p-type layer at an atmosphere including oxygen, (c) performing cleaning treatment for removing an oxidation film that is formed on a surface of the semiconductor layers during processes of the activation treatment, (d) forming a current diffusion layer on a surface of the p-type layer that has been purified during processes of the cleaning treatment, (e) removing a part of the current diffusion layer and laminated semiconductor layers through etching to expose the n-type layer, and (f) forming electrodes on the exposed n-type layer and on the p-type layer, respectively in an electrical connected manner.
In this manner, oxidation will not progress as far as to the interior though an oxidation film may be formed on the surface of the semiconductor layers by performing heat treatment in the presence of oxygen, and by purifying the surface through cleaning treatment, the adhesion with the current diffusion layer can be improved so that the electric resistance at the interface can be sufficiently decreased.
In case the atmosphere including oxygen is an air atmosphere or an atmosphere partially containing air in inert gas, the activation treatment can be performed in an ordinary heat treatment furnace.
REFERENCES:
patent: 4391854 (1983-07-01), Kanda et al.
patent: 5771110 (1998-06-01), Hirano et al.
patent: 5821158 (1998-10-01), Shishiguchi
patent: 5851842 (1998-12-01), Katsumata et al.
patent: 5963787 (1999-10-01), Kimura et al.
Arent Fox Kintner & Plotkin & Kahn, PLLC
Pham Long
Rohn Co., Ltd.
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