Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus – For crystallization from liquid or supercritical state
Reexamination Certificate
1999-05-09
2001-05-08
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Apparatus
For crystallization from liquid or supercritical state
C117S218000, C117S911000, C117S932000
Reexamination Certificate
active
06228167
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a single crystal pulling apparatus for producing a dislocation-free single crystal of silicon (Si) by the pulling Czochralski method.
BACKGROUND ART
In general, in a single crystal manufacturing apparatus based on the pulling Czochralski method, the pressure inside a highly pressure proof airtight chamber is reduced to about 10 torr and fresh argon (Ar) gas is sent into it. Then, polycrystal in a quartz crucible placed in the lower portion of the chamber is heated and melted. Then, seed crystal is immersed into the surface of the melt from above, and the seed crystal is pulled while rotating and moving up and down the seed crystal and the quartz crucible. As a result, a single crystal (the so-called ingot) is grown, which comprises an upper cone portion in conical shape with its upper end protruding below the seed crystal, a body portion in cylindrical shape, and a lower cone portion in conical shape with its lower end protruding.
As the growing method, Dash method is known, in which a seed crystal is immersed into the surface of the melt to exclude dislocation (to turn to dislocation-free) which occurs to the seed crystal by thermal shock when the seed crystal is immersed in the surface of the melt. Then, pulling rate is relatively increased to form a neck portion with diameter smaller than the-diameter of the seed crystal, e.g. 3-4 mm, and pulling of the upper cone portion is started.
Because it is not possible to pull single crystal of larger diameter and heavier weight (150-200 kg or more) via the neck portion with small diameter, a method has been proposed, for example, in the Japanese Patent Publication 5-65477. According to this method, a neck portion with smaller diameter is formed by Dash method, and pulling rate is then relatively slowed down to form a portion with larger diameter. Then, the pulling rate is relatively increased to form a portion with smaller diameter, i.e. to form a “spherical constricted portion”, and by gripping the constricted portion by grippers, single crystal of larger diameter and heavier weight is pulled up. Also, as a conventional apparatus for gripping the constricted portion, there are the apparatuses described in the Japanese Patent Publications 7-103000 and 7-515 in addition to the above patent publication.
As the other conventional examples, the following methods have been proposed: a method to grip a body portion without forming the “constricted portion” as shown in the Japanese Patent Publication Laid-Open 5-270974 or 7-172981, or a method to form “an annular constricted portion” with diameter larger than the body portion between the upper cone portion and the body portion and to grip this “annular constricted portion”.
However, single crystal pulling process is a process, which is very sensitive to external vibration and which is very likely to cause polycrystal. Therefore, in single crystal pulling operation, there is a problem of how to move self-weight of the crystal in smooth and soft manner to gripping position such as constricted portion or the neck portion. Also, because of high temperature in the pulling furnace, gripping mechanisms and the like must be designed in heat-resistant construction. Further, intermingling of particles (dust) must be avoided as much as possible because this deteriorates quality of the crystal. None of the conventional techniques has definitely solved these problems. In the Japanese Patent Publications Laid-Open 5-270974, 5-270975, and 5-301793, the seed crystal pulling-mechanism and the gripper pulling mechanism have different driving sources, and there is neither disclosure nor suggestion as to how synchronous operation of these mechanisms can be attained.
In the Japanese Patent Publication Laid-Open 9-2893, the seed crystal pulling mechanism and the gripper pulling mechanism have different driving sources, and it is disclosed that these are synchronously operated or independently operated. However, in case of synchronous operation, the control process is complicated, and the apparatus used for control is complicated in structure and high in cost. Further, in the Japanese Patent Publication 7-515, it is disclosed that a vertical moving mechanism for engaging the grippers with constricted portion of single crystal is provided on a shaft to form the seed crystal pulling mechanism. After engagement, the grippers are also pulled up in synchronization with the seed crystal merely by the control of the seed crystal pulling mechanism. However, there is neither disclosure nor suggestion on effective means to stop the engaged portion, and it is difficult to use in practical application. Also, according to the Japanese Patent Publication 7-515 and the Japanese Patent Publication Laid-Open 7-172981, screw units and mechanical driving units in the driving mechanisms have metal components coming into contact with each other, and these are arranged in the pulling furnace maintained at high temperature. For this reason, it is difficult to take heat-resistant measures or mechanical units do not satisfactorily fulfill the function. Further, particles generated from mechanical contact parts may give adverse influence, and this hinders single crystal pulling operation.
According to the Japanese Patent Publication Laid-Open 9-2893, all driving mechanisms are arranged outside the vacuum chamber to avoid the problem of intermingling of particles into the pulling furnace under high temperature condition. By synchronous control of seed crystal pulling rate and gripping mechanism pulling rate, it is attempted to solve all problems found in the conventional type apparatus at once. However, the synchronous control can be achieved by mutually adjusting the pulling rate of wire drum to wind up seed crystal pulling wire and the pulling rate of the pulling drive, to which gripping means are connected. In this respect, the control mechanism and the control process are complicated and the cost for designing and manufacture of the apparatus is high, and it is also difficult to perform maintenance.
DISCLOSURE OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a single crystal pulling apparatus having relatively simple arrangement and manufactured at low cost, by which it is possible to prevent the single crystal being pulled from turning to polycrystal when it is gripped by grippers, to move self-weight of the crystal from the neck portion to the gripping position such as constricted portion in smooth and soft manner during single crystal pulling operation, and to avoid the problem of the influence of high temperature and of the intermingling of particles.
To attain the above object, according to the present invention, the position of gripping members to be engaged with the portion with larger diameter formed under the seed crystal is controlled in vertical direction with respect to the seed crystal holder, and when it is out of the vertical position control operation, the gripping members are moved integrally with the seed crystal holder in vertical direction by transmitting motive power of the seed crystal pulling means, and the driving mechanisms are arranged outside the vacuum chamber for storing the crucible and the single crystal to be grown.
According to another aspect of the present invention, the portion with larger diameter formed under the seed crystal is supported from below and a support base is used as a dish-like member to hold the portion with larger diameter, position of the support base is controlled in vertical direction with respect to the seed crystal holder, and when it is out of the vertical position control operation, the support base is moved integrally with the seed crystal holder in vertical direction by transmitting motive power of the seed crystal pulling means, and all driving mechanisms are arranged outside the vacuum chamber for storing the crucible and the single crystal to be grown.
The present invention provides a single crystal pulling apparatus, which comprises:
rotating means for rotating a seed crys
Iida Tetsuhiro
Kuramoto Makoto
Champagne Donald L.
Connolly Bove Lodge & Hutz
Kunemund Robert
Super Silicon Crystal Research Institute Corp.
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