Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1996-03-29
2003-09-09
Huang, Evelyn Mei (Department: 1625)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S285000, C438S590000, C438S478000, C438S930000, C438S648000, C117S090000, C117S094000, C117S097000, C117S102000, C117S104000, C117S106000, C117S952000
Reexamination Certificate
active
06617235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a method of manufacturing a Group III-V compound semiconductor by thermal decomposition vapor phase method using metalorganics.
2. Description of the Background Art
Since Group III-V compound semiconductors which are expressed by a general formula In
x
Ga
y
Al
z
N (0≧x≧1, 0≧z≧1, x+y+z=1) have a band gap which can be controlled by the composition of Group III elements, Group III-V compound semiconductors can be used as a light emitting element which emits light ranging from the visible range to the ultraviolet range. In addition, since Group III-V compound semiconductors have a band structure of the direct transition type, using a Group III-V compound semiconductor, it is possible to obtain a light emitting element which has a high luminescence efficiency. Group III-V compound semiconductors in which the concentration of In is 10% or more, in particular, are important for display applications, since the violet range or the longer visible wavelength range can be used as an emission wavelength.
A popular method of manufacturing Group III-V compound semiconductors is molecular beam epitaxy (hereinafter abbreviated as “MBE” in some cases), metalorganic vapor phase epitaxy (hereinafter abbreviated as “MOVPE” in some cases), etc. The MOVPE method is a method in which material gas is sprayed onto a heated substrate together with carrier gas so as to grow crystal due to thermal decomposition of the materials. Allowing crystals to grow uniformly over a wide area at a high accuracy, this method is industrially important as a manufacturing method. In the MOVPE method, hydrogen is often used as carrier gas since hydrogen is cheap gas with a high purity. This is because very pure hydrogen is relatively easily obtained by passing hydrogen through a palladium film.
Further, to efficiently inject a current into a semiconductor light emitting element with a low applied voltage, a p-type semiconductor and an n-type semiconductor are generally used as a current injection layer for holes and a current injection layer for electrons, respectively. However, in such a compound semiconductor manufactured by MOVPE, it is known that it is difficult to control the p-type conductivity while it is relatively easy to control the n-type conductivity. That is, even if doped with p-type impurities, the compound semiconductor has a high resistance. In general, therefore, the compound semiconductor is processed after grown, by electron beam irradiation, thermal annealing, etc., so that the compound semiconductor of the p-type conductivity has a low resistance.
Hence, while it is essential to perform such post-processing to manufacture an element which has a high current injection characteristic, such post-processing unavoidably deteriorates the yield. Moreover, a layer which contains the p-type impurities needs be located at the top and the layer must not be thick to render the post-processing effective, which serves as a restraint to the structure of the element.
Japanese Patent KOKAI (Laid-open) No. 6-232451 discloses that it is possible to grow p-type GaN, without performing any special post-processing, if grown by a method in which material gas is pressed against a substrate by second carrier gas which is blown from a direction which is perpendicular to a direction of supplying the material gas (hereinafter abbreviated as “TFMOCVD” in some cases). Still, this method aims at growing Mg-doped GaN on InGaN which was already grown, and therefore, the Mg-doped GaN does not exhibit the p-type conductivity if an InGaN layer is not used, according to the gazette.
Accordingly, an object of the present invention is to provide for a method of manufacturing a Group III-V compound semiconductor, which grows a nitrogen-contained Group III-V compound semiconductor of the p-type conductivity, without performing any particular post-processing after growing the compound semiconductor, and which prevents a deterioration in the yield of manufacturing light emitting elements due to post-processing.
SUMMARY OF THE INVENTION
Having studied the problems above and found that when inert gas other than hydrogen is mainly used as carrier gas, a compound semiconductor which contains p-type impurities exhibits the p-type conductivity even if the semiconductor is not processed by any particular post-processing, the inventors have arrived at the present invention. In other words, the present invention is related to the following:
[1] A method of manufacturing a Group III-V compound semiconductor which contains p-type impurities and which is expressed by a general formula In
x
Ga
y
Al
z
N (0≧x≧1,0 ≧y≧1,0≧z≧1,x+y+z=1), by thermal decomposition vapor phase method using metalorganics, the method being characterized in that carrier gas is inert gas in which the concentration of hydrogen is 0.5% or smaller by volume.
[2] A method of manufacturing a Group III-V compound semiconductor which contains p-type impurities and which is expressed by a general formula In
x
Ga
y
Al
z
N (0≧x≧1,0≧y≧1,0≧z≧1, x+y+z=1), by thermal decomposition vapor phase method using metalorganics, the method being characterized in that after etching within a reaction furnace using at least one compound which is selected from a compound group consisting of compounds of halogenated hydrogen, compounds of halogen and Group V elements, and compounds of halogen, hydrogen and Group V elements, inert gas in which the concentration of hydrogen is 0.5% by volume is used as carrier gas.
[3] The method of manufacturing a Group III-V compound semiconductor as described in the paragraph [1] or [2], characterized in that when there are two or more inlets for introducing carrier gas and/or material gas, the maximum angle between any two of the inlets and any point on the substrate is 80 degrees or smaller.
[4] The method of manufacturing a Group III-V compound semiconductor as described in the paragraph [1],[2] or [3], characterized in that the concentration of hydrogen is maintained at 0.5% or smaller by volume in the atmosphere, during a reduction in the temperature of a Group III-V compound semiconductor after the Group III-V compound semiconductor is grown.
Now, the present invention will be described in detail.
In the present invention, the gas contains 0.5% of or less hydrogen by volume. If the carrier gas contains more than 0.5% of hydrogen by volume, the p-type conductivity is not good enough, which is not desirable. Reducing the concentration of hydrogen in the carrier gas, the larger p-type carrier concentration and hence the better characteristics as a p-type semiconductor are achieved. A preferable concentration of hydrogen is 0.3% or less, more preferably, 0.1% or less, and most preferably, 0.04% or less.
Further, even if carrier gas which does not contain hydrogen is used while growing a semiconductor, the semiconductor may not exhibit the p-type conductivity in some cases if the atmosphere contains hydrogen while the semiconductor is cooled down. Hence, the concentration of hydrogen in the atmosphere during cooling down is preferably low. Reducing the concentration of hydrogen in the atmosphere, the larger p-type carrier concentration and hence the better characteristics as a p-type semiconductor are achieved. A preferable concentration of hydrogen is 0.3% or less, more preferably, 0.1% or less, and most preferably, 0.04% or less.
In general, a compound semiconductor grows at a high temperature such as 800° C. or more, and therefore, it is desirable to add Group V materials such as ammonia into the carrier gas while the temperature is not sufficiently lowered yet after growing the semiconductor, so as to suppress decomposition of the semiconductor due to heat. For this purpose, a preferable concentration range of Group V material in the growth atmosphere is 0.1% to 95%.
The inert gas, which mainly for
Iyechika Yasushi
Ono Yoshinobu
Takada Tomoyuki
Huang Evelyn Mei
Sumitomo Chemical Company Limited
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