Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With pretreatment or preparation of a base
Reexamination Certificate
2000-06-29
2002-11-05
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With pretreatment or preparation of a base
C117S108000, C117S200000, C118S7230VE
Reexamination Certificate
active
06475277
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a growth method and vapor phase growth apparatus for group III-V nitride semiconductors such as gallium nitride (GaN).
2. Related Background Art
conventionally known as a method of growing group III-V nitride semiconductors such as GaN are, for example, a hydride vapor phase epitaxy method (HVPE method) published in Japanese Patent Application Laid-Open No. HEI 10-215000 and an organic metal vapor phase epitaxy method (OMVFE method) published in Japanese Patent Application Laid-Open No. SHO 61-179527.
For growing gallium nitride (GaN) by the hydride vapor phase epitaxy method, (1) ammonia (NH
3
) as a material gas for nitrogen (N), (2) hydrogen chloride (HCl) for generating gallium chloride (GaCl) as a material gas for gallium (Ga) and (3) hydrogen (H
2
) as a carrier gas are continuously introduced into a reaction ampoule in which a boat containing Ga is disposed. AS GaCl, which is generated by a reaction between HCl and Ga, reacts with NH
3
, gallium nitride (GaN) grows on a seed crystal, According to this method, a large amount of material gases can be continuously supplied into the reaction ampoule, whereby the reaction rate can be improved as compared with the case using a so-called closed ampoule method in which no material gases are supplied from the outside.
For growing gallium nitride (GaN) by the organic metal vapor phase epitaxy method, (1) an organic metal such as trimethyl gallium (TMG) and (2) ammonia (NH
3
) are introduced as material gases into a reaction ampoule, whereas hydrogen or nitrogen is introduced therein as a carrier gas. AS TMG and NH
3
react with each other, gallium nitride (GaN) grows on a seed crystal. According to this method, all the materials can be introduced into the reaction ampoule in the form of gas, whereby the film thickness can be controlled more precisely as compared with the hydride vapor epitaxy growth method.
SUMMARY OF THE INVENTION
However, the above-mentioned conventional hydride vapor epitaxy growth method and organic metal vapor phase epitaxy method have problems as follows. Namely, if group III-V compound semiconductors such as GaN are grown by the hydride vapor phase epitaxy method and organic metal vapor phase epitaxy method, then chlorine and hydrogen, which are no components of the group III-V compound semiconductors, will remain in the reaction ampoule as HCl, NH
3
, H
2
and the like, which are required to be let out of the reaction ampoule via an outlet. Namely, a so-called open ampoule method is employed in the hydride vapor epitaxy growth method and the organic metal vapor epitaxy growth method. As a consequence, most of the materials do not contribute to the growth and are discarded, whereby these methods are problematic in that the material efficiency is low. Also, for discarding a large amount of HCl, NE
3
, H
2
, and the like, a large-scale detoxification system is needed, which increases the cost. Namely, these methods are not suitable for making single crystals at a low cost.
In the so-called closed ampoule method, on the other hand, byproducts and the like are not let out, whereby the material efficiency is not so low as that in the hydride vapor epitaxy growth method and the organic metal vapor epitaxy growth method- However, while the growth rate has been required to improve in the field of making III-V compound semiconductors in recent years, no improvement in growth rate is expected in the closed ampoule method in which no material gases are supplied from the outside, since the amount of transportation of material gases is small.
In view of such circumstances, it is an object of the present invention to provide a group III-V nitride semiconductor growth method and vapor phase growth apparatus having a high material efficiency and a high growth rate.
In one aspect, the present invention provides a group III-V nitride semiconductor growth method for growing a group III-V nitride semiconductor on a seed crystal disposed within a reaction ampoule, the method comprising the steps of plasma-exciting nitrogen continuously introduced into the reaction ampoule and evaporating a group III element disposed within the reaction ampoule; and causing thus plasma-excited nitrogen and evaporated group III element to react with each other, so as to grow the III-V nitride semiconductor on the seed crystal.
In the group III-V nitride semiconductor growth method in accordance with this aspect of the present inventions nitrogen (N
2
) introduced into the reaction ampoule is excited so as to attain a plasma state, whereas a group III (group
3
B) element such as gallium (Ga), for example, is evaporated within the reaction ampoule. As thus plasma-excited nitrogen and evaporated group III element react with each other, a group III-V nitride semiconductor such as gallium nitride (GaN)), for example, can be grown on the seed crystal. Here, since nitrogen is excited so as to attain a plasma state in this aspect of the present invention, it is more likely to react with the group III element as compared with a nitrogen molecule state in which the bonding strength between atoms is higher, and it can successively be introduced into the reaction ampoule unlike the case employing the closed ampoule method, whereby the growth rate of group III-V nitride semiconductor can be enhanced. Also, in this aspect of the present invention, only the group III element and nitrogen are used for growing the group III-V nitride semiconductor, and all the group III element and nitrogen contribute to growing the group III-V nitride semiconductor. Namely, no byproducts are generated upon growing the group III-V nitride semiconductor, whereby it is unnecessary to let out gases from within the reaction ampoule, whereby the material efficiency can be improved.
Preferably, in this aspect of the present invention, positive and negative pulsed voltages are alternately applied between two electrodes, so as to plasma-excite nitrogen between the electrodes.
In this case, since the positive and negative pulsed voltages are applied between the electrodes, an intermittent signal with a break between individual pulses is generated, whereby, as compared with the case where a continuous sine wave of high-frequency voltage is applied, the discharging phenomenon would not yield corona discharge, and nitrogen is more likely to be plasma-excited.
In another aspect, the present invention provides a group III-V nitride semiconductor growth method for growing a group III-V nitride semiconductor on a seed crystal disposed within a reaction ampoule, the method comprising the steps of causing nitrogen continuously introduced into the reaction ampoule to react with hydrogen within the reaction ampoule upon plasma excitation, so as to generate a hydride of nitrogen, and causing the hydride of nitrogen and a group III element evaporated within the reaction ampoule to react with each other, so as to grow the group III-V nitride semiconductor on the seed crystal; and then causing hydrogen generated upon growing the group III-V nitride semiconductor and nitrogen continuously introduced into the reaction ampoule to react with each other upon plasma excitation, so as to generate a hydride of nitrogen.
In the group III-V nitride semiconductor growth method in accordance with this aspect of the present invention, nitrogen continuously introduced into the reaction ampoule is caused to react with hydrogen within the reaction ampoule by plasma excitation, so as to generate a hydride of nitrogen such as NH, NH
2
, NH
3
, or the like. Within there action ampoule, on the other hand, a group all element such as gallium, for example, is evaporated. Then, the hydride of nitrogen and thus evaporated group III element react with each other, so that a group III-V nitride semiconductor such as gallium nitride grows on the seed crystal. Here, in this aspect of the present invention, since nitrogen diffuses into the vicinity of the seed crystal as a hydride such as NH
x
(X=1 to 3) and reacts with the group III ele
Hirota Ryu
Tatsumi Masami
Kunemund Robert
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
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