Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Liquid phase epitaxial growth
Reexamination Certificate
1993-05-05
2001-08-14
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Liquid phase epitaxial growth
C117S059000, C118S409000, C118S416000
Reexamination Certificate
active
06273946
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a method and apparatus for producing a multi-layered epitaxial crystal useful as a semiconductive material.
TECHNICAL BACKGROUND OF THE INVENTION
As a method for simultaneously performing a liquid-phase epitaxial growth on the surfaces of a plurality of crystalline substrates, there has been known a process wherein a plurality of crystalline substrates are received in a holder in such a manner that they are arranged in a state faced to each other with predetermined intervals along an approximately vertical direction, the gaps between the crystalline substrates are filled with a melt for crystal growth maintained in a saturated state at a high temperature or in a supersaturated state by slightly lowering the temperature, and the melt is held in contact with the surface of each crystalline substrate to deposit an epitaxial layer on the surface of each crystalline substrate by proper temperature control such as slow cooling.
In a liquid-phase epitaxial crystal growth process, it is comparatively easy to epitaxially grow only one layer on the surface of each crystalline substrate. As the most principal means for this purpose, there have been developed various methods so far, wherein an alignment of the substrates is lowered and dipped into a melt maintained at a lower position with respect to the alignment of the crystalline substrates, to bring out crystal growth on the surface of each substrate, and then the alignment of the substrates are raised and separated from the melt.
There is, for example, a known method wherein an alignment of crystalline substrates are supported with an eccentric rotary shaft in a manner such that the crystalline substrates are dipped in the melt and then separated from the melt using the rotation of the eccentric rotary shaft. In another method, a melt is pumped by a piston and brought into contact with the alignment of crystalline substrates located at a higher position.
In these known methods, however, the melt is circulated relatively upwards to the gaps between adjacent crystalline substrates, and then let flow down after the growth of a proper crystalline layer. But, since the oxide films and microcrystals deposited from the melt are floating on the surface of the melt or suspending in the upper layer of the melt, the oxide films and/or microcrystals are apt to adhere onto the surface of an grown layer during dipping and lifting the substrate. The adhesion of the oxide films and/or microcrystals, i.e. the contaminated surface of the epitaxial layer, causes troubles on the growth of a normal crystal layer thereon, especially when the growth of a second or more layers are performed in the succeeding steps.
When the next crystal growth for the second layer is performed by further bringing the first epitaxial layer contaminated with the oxide films and/or the microcrystals into contact with another melt for the second layer, there will occur stacking faults originated in the part where the oxide films and/or the microcrystals adhered. In the case where the oxide films and/or the microcrystals exhibit significant influences, said part becomes to an upgrowth pit. Epitaxial layers involving such defects are not proper for the formation of electronic devices. Even if the electronic devices are formed using the said materials, the obtained products would exhibit very low performances and lack in reliabilities.
The influence of the defects will become larger when the third or more layers are further piled up in a multi-layered state. The uppermost layer substantially lacks in flatness, hence the multi-layered crystals can not be handled just for the process of producing electronic devices.
As above-mentioned, the influence of oxide films and/or microcrystals floating on the surface of a melt is inevitable in the liquid-phase epitaxy method, as far as the melt is circulated relatively upwards into the gaps between adjacent crystalline substrates and then let flow down after the growth of a proper crystalline layer.
In order to eliminate the aforementioned defects, there is known another method as shown in
FIG. 1
, wherein a melt is supplied from above the alignment of crystalline substrates.
With reference to
FIG. 1
, a holder b for receiving the alignment of crystalline substrates is provided in a horizontal tubular electric resistance furnace a. A reservoir c for reserving a melt to be used for crystal growth is located above the holder b, while a reservoir d for receiving the melt used for the crystal grow this located below the holder b. The reservoirs c and d are faced to each other along a vertical direction, and an upper shutter blade e and the lower shutter blade f are disposed between the reservoirs c and d, the upper shutter blade e and lower shutter blade being in a state each capable of sliding along the axial direction of the furnace a. The upper shutter blade e has a circulation hole h formed through its thickness to let a melt g flow down through the upper shutter blade e.
When the circulation hole h of the upper shutter blade e is brought to the position corresponding to a hole formed in the bottom wall of the reservoir c by the movement of the upper shutter blade e, the melt g is let to flow down from the reservoir c and poured in the holder b. Hereon, only the lower layer of the melt g in the reservoir c flows down to the holder b, while the upper layer of the melt g contaminated with formed oxide films and/or deposited microcrystals remains as such in the reservoir c. Consequently, the holder b is filled with the pure melt g free from inclusions. The alignment i of crystalline substrates in the holder b comes in contact with the uncontaminated pure melt g, so that a proper epitaxial layer grows on the surface of each substrate.
After the completion of the epitaxial growth, the lower shutter blade f is carried to the position where a circulation hole j formed in the lower shutter blade f comes to the position corresponding to a discharge hole formed in the bottom wall of the holder b. The used melt g in the holder b flows down to the reservoir d, and the alignment of the crystalline substrate is released from the condition in contact with the melt g.
The shutter blades e and f are individually carried along the axial direction of the furnace a by operating rods k. The reservoir c for the melt g to be used for crystal growth is carried along the axial direction inside the furnace a by another operating rod l. A reaction zone for the crystal growth is isolated from the outside atmosphere by a quartz tube m.
When the melt g for the crystal growth is let flow down, brought into contact with the alignment i of crystalline substrates and then discharged downwards to the used melt reservoir d as above-mentioned, a contaminated melt containing oxide films and/or microcrystals is prevented from flowing into the holder b. Therefore, the formation of crystallographic defects derived from the oxide films and/or the microcrystals can be inhibited.
In order to apply this method to a process for the production of multi-layered crystals, it is necessary to provide a plurality of reservoirs c for reserving various kinds of melts above the holder b receiving the alignment i of crystalline substrates therein in the order of crystal growth steps. Hereon, in a commonly adopted manner, the holder b is stationarily held at an approximately central position with respect to the axial direction of the furnace a, while reservoirs c for receiving a plurality of melts are slidingly disposed right-side and/or left-side above the holder b. Each melt is different in the kind of a dopant, concentration, and composition for determining the mixing ratio of a deposited layer from the other. The reservoirs c are intermittently carried to a position above the holder b in the order of crystal growth steps.
The reservoirs c for the melts to be used for crystal growth are arranged in series above the horizontal tubular electric resistance furnace a to intermittently pour the melts to the holder b. This arrangement requ
Kurata Kazuhiro
Nakamura Hajime
Tomida Hiroshi
Arent Fox Kintner Plotkin & Khan, PLLC
Kunemund Robert
Nisshin Steel Co. Ltd.
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