Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Liquid phase epitaxial growth
Reexamination Certificate
2002-08-28
2004-11-30
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Liquid phase epitaxial growth
C117S204000, C117S206000, C117S900000
Reexamination Certificate
active
06824609
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid phase growth method for producing various semiconductor crystals and optical crystals adapted for use in semiconductor devices and electro-optical devices, and a liquid phase growth apparatus suitable for carrying out the method.
2. Related Background Art
Solar cells have become adopted widely for consumer use with the recently increased concern for the environment. Monocrystalline or polycrystalline silicon is principally used as the semiconductor material for the solar cells for consumer use.
At present, such crystals are cut out from a large ingot by slicing in the form of a wafer of a thickness of about 300 &mgr;m. Such a method is insufficient in the utilization efficiency of the material, since a slicing margin of about 200 &mgr;m will be required in the slicing operation. In order to attain a larger production amount and a lower cost hereafter, it is desired to grow and use a crystal of a minimum thickness required electrically or optically of several 10 to about 100 &mgr;m. For growing a crystalline silicon of such a small thickness, there has principally been investigated the gaseous phase growth method in which a silicon-containing gas is decomposed by the action of heat or plasma.
However, in the mass production of solar cells, there is required an apparatus capable of growing silicon at a rate of 1 &mgr;m/min or more on several tens to several hundreds of square substrates of 4 to 5 inches square in a single batch. The gaseous phase growth apparatus that meets such requirement is not commercially available.
For crystal growth, there is also conventionally known the liquid phase growth method, and the method is practically employed in producing compound semiconductor crystals for LEDs and optical crystals for electro-optical elements. Recently, as disclosed in Japanese Patent Application Laid-Open No. 10-189924, there has been reported utilization of a crystalline silicon film grown on a crystalline silicon substrate or a ceramic substrate for the production of the solar cells.
In the liquid phase growth method, a melt is prepared firstly by heating to fuse a metal such as tin, indium or gallium or an oxide such as a lithium oxide or niobium oxide. Then, a material for constituting a crystal such as arsine or silicon is melted in the melt as needed, then a substrate is dipped in the melt and the melt is brought into supersaturation by, for example, cooling to deposit a crystal on the substrate. The liquid phase growth method is not only capable of growing a crystal of good quality but also is less in the waste of a material that does not contribute to the crystal growth as compared with the gaseous phase growth method and is therefore suitable for application to a device such as a solar cell for which a low production cost is strongly required or an electro-optical device using an expensive material such as gallium or niobium.
However, since the liquid phase growth method has been limited in its application, the apparatuses that have been commercially available are limited to those for growing a compound semiconductor on a substrate of 3 inches or less in diameter and have had few applications for silicon growth.
In consideration of the foregoing, the conventional liquid phase growth apparatuses have been studied and found to have the following problems.
FIG. 14
is a schematic view showing an example of the conventional liquid phase growth apparatus capable of crystal growth on a plurality of substrates. In this apparatus, five substrates
201
are horizontally supported at predetermined distances by substrate support means
202
, and are immersed in a melt
204
held in a crucible
203
of a cylindrical shape with a bottom, and these components are housed in a growth chamber
205
. The temperature of the melt
204
can be suitably controlled by an electric furnace
206
. The growth chamber is provided with and can be suitably opened or closed by a gate valve
207
.
In this apparatus, firstly, substrates
201
′ for melting in a melt (represented as “
201
′” with a prime in order to distinguish them from substrate for crystal growth and hereinafter sometimes referred to simply as “melting substrates”) made of a crystal raw material (i.e., material to be grown) such as silicon are supported by the substrate support means
202
, and are immersed in a melt of a low-melting metal such as tin, indium or gallium or an oxide such as a lithium oxide or niobium oxide, as heated to a predetermined temperature by the electric furnace
206
, to melt the crystal raw material to the saturation state at the temperature, thereby preparing the melt
204
. Thereafter, the melting substrates
201
′ are lifted up from the melt
204
and are replaced by the substrates
201
for crystal growth (hereinafter sometimes referred to simply as “growth substrates”). (Therefore, the growth substrate
201
and the melting substrate
201
′ cannot be distinguished from each other in the figures.)
Thereafter, when the melt
204
is gradually cooled to a predetermined temperature and the growth substrates
201
are immersed therein, the raw material which is no longer soluble in the melt
204
starts to deposit on the surfaces of the substrates
201
, so that crystals such as of silicon will grow on the substrates. At this time, a polycrystalline film is grown when the substrate
201
is made of polycrystalline silicon, glass or ceramic, but a monocrystalline film can be grown when the substrate
201
is made of monocrystalline silicon. The substrates
201
are lifted up when the crystals are grown to a predetermined thickness.
By carrying out the mounting or detaching of the substrates
201
to or from the substrate support means
202
with the gate valve
207
being closed, and by changing the interior of the load lock chamber
208
from the atmosphere to an inert gas or the like and thereafter opening the gate valve
207
and lowering the substrates
201
into the growth chamber
205
, the melt
204
can be prevented from reacting with oxygen or water or from being contaminated.
In the apparatus shown in
FIG. 14
, the number of substrates can be increased as needed. However, it has been experimentally found that the above-described configuration is insufficient for obtaining a high growth rate uniformly over the plane.
FIG. 15
is a chart showing the in-plane distribution of the growth rate in a case where five silicon wafers of a diameter of 5 inches, maintained at a mutual distance of 1 cm, are subjected to silicon crystal growth from an indium melt. In the figure, the symbol “∘” indicates the distribution in the substrates positioned close to the surface layer portion of the melt, while “•” indicates that in the substrates positioned close to the bottom of the melt.
Although the difference between the substrates is small, the growth rate at the central portion of each substrate is about ⅓ of that at the peripheral portion, as shown in FIG.
15
. Further, decreasing the cooling rate of the melt reduces the ununiformity within the plane but also decreases the entire growth rate. Further, increasing the distance between the substrates reduces the ununiformity but decreases the number of substrates that can be charged in a single batch. Thus, the both means will result in lowering in the throughput.
The ununiformity of the growth rate within the plane results from the fact that a fresh melt cannot be supplemented in a sufficient amount after the crystallization of the semiconductor raw material melted in the melt present between the substrates, and the ununiformity becomes more remarkable as the deposition rate becomes large or the distance between the substrates is made smaller. In the apparatus shown in
FIG. 14
, by rotating the substrates during the crystal growth, the uniformity of the growth rate is somewhat improved since a melt containing silicon at a high concentration is supplemented between the substrates, but is still insufficient.
For causing mutu
Mizutani Masaki
Nakagawa Katsumi
Nishida Shoji
Saito Tetsuro
Shoji Tatsumi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hiteshew Felisa
LandOfFree
Liquid phase growth method and liquid phase growth apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid phase growth method and liquid phase growth apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid phase growth method and liquid phase growth apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3274829