Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus – For crystallization from liquid or supercritical state
Reexamination Certificate
2001-06-15
2003-05-13
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Apparatus
For crystallization from liquid or supercritical state
C117S011000, C117S224000
Reexamination Certificate
active
06562134
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a crystal growth apparatus comprising a heating furnace, which has a multi-stage heater. Particularly, it relates to a crystal growth apparatus of a compound semiconductor that requires a precise temperature control, and to an effective technology applied to a crystal growth method by using the crystal growth apparatus.
BACKGROUND ART
Generally, the vertical gradient freezing (VGF) method, vertical Bridgman (VB) method, horizontal gradient freezing (HGF) method and horizontal Bridgman (HB) method or the like have been known as methods for growing a compound semiconductor single crystal. In these methods, a compound semiconductor single crystal is grown by utilizing the temperature gradient in a growth furnace.
In a crystal growth apparatus to which such a growth method is applied, in order to realize the desired temperature gradient, there is a case that a heating furnace having a multi-stage heater is used. As an invention using a heating furnace having a multi-stage heater, there is, for example, the invention described in the International Publication No. WO95/22643. In this invention, by utilizing the VGF method, the temperature distribution in a heating furnace is controlled so that a first vertical temperature gradient in vicinity of the external wall of the quartz ampoule corresponding to a raw material melt may be smaller than a second vertical temperature gradient above the upper end of a crucible. Then, the temperature in the heating furnace is decreased gradually, for the crystal to be grown toward the lower side from a surface of the raw material melt.
Further, in the prior application, in order to control the temperature gradient accurately, a crystal growth apparatus comprising a heating furnace having at least six heating means (heaters), is suggested. A schematically sectional view of the crystal growth apparatus is shown in FIG.
5
. In
FIG. 5
, the crystal growth apparatus
100
comprises a heating furnace
110
having an upper stage heater portion
101
to
104
and a lower stage heater portion
105
to
107
, a control device, which controls the furnace internal temperature distribution or the like by controlling electric energy to each heater, and a power source device. A quartz ampoule
111
having a reservoir portion
111
A, in which a crucible
112
made of pBN and charged with a raw material
113
is sealed, is disposed in the heating furnace
110
. The heating furnace
110
comprises a heater
103
, which controls the first temperature gradient by heating the position corresponding to the crucible
112
, a heater
102
, which controls the second temperature gradient by heating the space above the upper end of the crucible
112
, a heater
106
, which controls the vapor pressure by heating the reservoir portion
111
A, heaters
101
and
107
, which suppress the influence of disturbance to the furnace internal temperature distribution, and heaters
104
and
105
, which suppress the mutual influence between the heater
103
and the heater
106
.
According to the crystal growth apparatus, since the heaters are in multi-stage, it is possible to control extremely satisfactorily the first temperature gradient and the second temperature gradient, and there is the advantage that the yield of a single crystal substrate can be improved rapidly.
However, in growth of a compound semiconductor single crystal by using the above-described crystal growth apparatus having a multi-stage heater, although it is possible to improve the yield of a single crystal substrate, when aiming at an inplane dopant (impurity) concentration of a obtained wafer, it was found by an experiment that there is dispersion at least beyond the measurement error in a plane.
The present inventors repeated eagerly researches about the case. When a crystal is grown by using the above-described crystal growth apparatus, the temperature distribution around the crystal was measured in the same horizontal plane along the circumferential direction, and only one place was evidently low, compared with the others. Then, the temperature distribution was compared with the inplane dopant concentration distribution of the wafer, and it was noticed that the temperature distribution is corresponding to the inplane dopant concentration distribution. Therefore, it is reached to the conclusion that solidifying process of a crystal is shifted in the same plane since the inplane temperature distribution of the heating furnace is not uniform, and consequently, dispersion of the inplane dopant concentration of the wafer occurs.
Furthermore, it is found that in the inplane temperature distribution in the furnace, the region that the temperature is low is corresponding to the position of the terminals of the heaters. Therefore, it is ascertained that heat radiation from the terminal portions of the heaters is the cause of the inplane temperature distribution in the furnace not being uniform. A perspective view of the upper stage heater portions
101
to
104
in
FIG. 5
, is shown in FIG.
6
. The heaters and a power source device or a control device are connected through wirings. However, in the conventional crystal growth apparatus, the terminal portions
101
a
to
104
a
, which are taken out from each heater, were always disposed in the same place on the circumference, seeing from the axial direction of the heating furnace, in order to be wired easily. In this case, since there is heat radiation from the terminal portions, the furnace internal temperature in vicinity of the terminal portions was decreased somewhat, so that the temperature distribution in the same horizontal plane in the furnace was dispersed delicately.
The present invention was made to solve the problem. The objects of the invention are to provide a crystal growth apparatus comprising a heating furnace, which can control the temperature distribution in the same horizontal plane in the furnace, and to provide a method for producing a single crystal by using the crystal growth apparatus.
DISCLOSURE OF INVENTION
In order to accomplish the objects, in the present invention, a crystal growth apparatus comprises a cylindrical heating furnace having a multi-stage heater, and the inplane temperature distribution in a heating furnace is made to become uniform without gathering terminal portions taken out from each heater in one place.
Concretely, when the number of the heaters is, for example, two, each heater may be disposed so that the terminals may be located at an almost facing position. Further, when the number of the heaters is N (N is a positive integer of three or more), each heater may be disposed so that the terminal portions of the heaters may be located at each apex of a regular n-gon (n is an integer which satisfies 3≦n≦N), seeing from the axial direction of the heating furnace. Therefore, since heat radiation from the terminal portions does not occur at one place, it is possible to uniform the inplane temperature distribution in the heating furnace.
In order to grow a single crystal by using the crystal growth apparatus, for example, a heat-resistant container charged with a raw material is disposed in the heating furnace portion of the crystal growth apparatus. The heater is controlled and a predetermined temperature distribution is made in the furnace. Then, after melting the raw material by heating the heat-resistant container portion to be over the melting point of the raw material, the crystal is grown preferably by decreasing the temperature of the heating furnace gradually, while maintaining the temperature distribution. Thereby, the uniformity of the inplane dopant concentration of a wafer obtained can be improved sharply.
Further, a crystal growth apparatus of a compound semiconductor comprises a heating furnace having an upper stage heater portion heating a crucible portion charged with a raw material of a compound semiconductor, and a lower stage heater portion heating a reservoir portion communicated with a quartz ampoule sealing the crucible. The upper stage heater portion
Hichiwa Akira
Hirano Ryuichi
Kubota Yoshiaki
Maeda Hiroshi
Yamamoto Tetsuya
Birch & Stewart Kolasch & Birch, LLP
Hiteshew Felisa
Nikko Materials Co., Ltd.
LandOfFree
Crystal growing device and method of manufacturing single... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Crystal growing device and method of manufacturing single..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Crystal growing device and method of manufacturing single... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3036690