Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus – For crystallization from liquid or supercritical state
Reexamination Certificate
1998-10-06
2001-02-06
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Apparatus
For crystallization from liquid or supercritical state
C117S217000, C117S219000, C117S222000, C117S911000
Reexamination Certificate
active
06183556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to seed crystals and the seed chucks used to hold the seed crystals during growth. More particularly, the invention relates growing dislocation-free (DF) crystals.
2. Description of Related Art
The monocrystalline silicon that is the starting material for many semiconductor electronic components is commonly prepared by a Czochralski (CZ) process. In this process, pieces of polycrystalline silicon are placed in a crucible and melted to a liquidous state, thereby creating a melt. A seed crystal having the desired monocrystalline atomic structure is then lowered into contact with the molten silicon. As the seed crystal is slowly extracted from the melt, a monocrystalline crystal is drawn from the melt having the same atomic structure as the seed crystal. One such type of crystal pulling apparatus is disclosed in EP 783 047, which is incorporated by reference herein.
Unfortunately, dislocation defects are generated in the seed crystal due to thermal shock as the seed crystal contacts the relatively hot melt. If corrective actions are not taken, the dislocation defects propagate through and multiply in the growing crystal. As known to those skilled in the art, dislocations generally propagate along crystallographic planes. For a silicon seed crystal having a <100> orientation, the dislocations typically propagate along a plane that extends at an angle of 55° from the longitudinal axis of the crystal.
In order to terminate the dislocations prior to propagation through the main body of the crystal, crystals typically have a neck section extending between the seed crystal and the main body of the crystal. The most common method of eliminating dislocations is known as the Dash method and involves growing a neck having a relatively small diameter and a relatively long length. For example, a neck grown according to the Dash method may have a diameter of between 2 mm and 4 mm and a length between 30 mm and 200 mm. As the neck is grown, the dislocations propagate through the neck toward the interface of the seed crystal and the melt. As a result of the extended length and small diameter of the neck, however, the dislocations terminate at the exterior surface of the neck such that the main body of the crystal is dislocation-free (DF). The crystal is then expanded in diameter through the shoulder portion to the DF main body. Since there is no easy and reliable method to determine if the dislocations have been terminated, the Dash method generally requires the neck to have a relatively small diameter and an extended length in order to effectively terminate most, if not all, dislocations.
Although the Dash method is widely utilized, the Dash method has several significant disadvantages. For example, the time and expense associated with growing the neck section are non-recoverable since the neck is ultimately discarded as waste. Also, since the entire crystal is supported during growth by the relatively thin neck section, the maximum mass of a crystal is limited, typically to approximately 140 kg. Although this weight limit poses productivity and economic problems for crystals having conventional diameters of 150 mm or 200 mm, even more problems are created by this weight limit as the silicon industry begins to investigate and grow crystals having diameters of 300 mm or more.
To reduce the thermal shock, dipping speed has also been carefully controlled. Often the seed crystal will be lowered toward the melt and held slightly above the melt until the temperature of the seed crystal stabilizes. Such delay reduces efficiency and adds significant time to the process. Further external gases flowing toward the seed crystal cool the seed crystal, thus making it difficult to stabilize the temperature of the seed crystal.
Therefore, notwithstanding prior technique to grow DF crystals, a need still exists for an improved technique for growing DF crystals. In particular, a need exists for improved techniques for growing relatively large and heavy DF crystals without subjecting the neck of the crystal to excessive force and without repeatedly adjusting the pulling speed or requiring additional equipment for lifting or otherwise supporting the crystal during growth.
SUMMARY OF THE INVENTION
One aspect of the invention is to reduce or eliminate dislocations in seed crystals during growth.
Another aspect of the invention is to provide seed chucks that warm and insulate the seed crystals to thermally isolate or create a thermal barrier during growth in order to reduce thermally induced stress dislocations.
A further aspect of the invention is to warm and insulate the seed crystals using the seed chuck without the addition of external warming devices.
An additional aspect of the invention is to provide a method of growing seed crystals that have reduced or no dislocations.
Another aspect of the invention is to control the energy of the melt to warm the seed crystal by collecting and focusing emissive, reflective and conductive thermal energy of the melt and shield or redirect external gas flow from the seed crystal.
The invention is directed to a seed chuck for supporting a seed crystal for dipping in a hot melt. The seed chuck has a main body including a dipping support formation for connection to a dipping apparatus and a seed support formation for supporting a seed crystal. A shield is coupled to the main body that insulates the seed crystal from cooling and heats the seed crystal with radiant energy emitted from the hot melt.
The shield may be in the form of an insulating layer disposed against the main body of the seed chuck. The shield may also be a hollow portion of the seed chuck attached to the main body and having insulating material disposed therein. The shield may be insulating inserts disposed between the seed crystal and the seed chuck to thermally isolate the seed crystal. In this case, the seed crystal is insulated from the cooler seed chuck and allowed to be warmed by the hot melt.
The shield may also be a removable flange extending outwardly from the seed chuck. The flange may have an inverted cup shape or parabolic umbrella shape. The curve of the flange may be varied depending on where the heat radiating from the hot melt is desired to be reflected onto the seed crystal. The shield contains the heat radiating from the hot melt and concentrates the radiation in the area surrounding the seed crystal. The inner surface of the shield facing the seed crystal may be coated with a reflective coating to increase efficiency. The shield in this case may also be insulated or made of insulating material. Thus, the shield prevents cooling external gas flow from reaching the seed crystal while capturing and directing heat radiating from the hot melt onto the seed crystal.
The method of warming the seed crystal during a growth process in which the a portion of the seed crystal is dipped in a hot melt includes providing a hot melt consisting of a molten mass of material, supporting the seed crystal in a seed chuck for selectively lowering the seed crystal into the hot melt, and warming the seed crystal supported in the seed chuck by using heat radiating from the hot melt and by insulating the seed crystal from external cooling forces.
Other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which taken in conjunction with the annexed drawings, disclosed preferred embodiments of the invention.
REFERENCES:
patent: 4594127 (1986-06-01), Lane et al.
patent: 5759261 (1998-06-01), Dornberger et al.
patent: 5833750 (1998-11-01), Mizuishi et al.
patent: 5865887 (1999-02-01), Wijaranakula et al.
patent: 229 722 A1 (1985-11-01), None
patent: 0 769 577 A2 (1997-04-01), None
patent: 0 783 047 A1 (1997-07-01), None
patent: 0 792 953 A1 (1997-09-01), None
patent: 58-50959 (1983-11-01), None
patent: 61-10098 (1986-01-01), None
patent: 63-156092 (1988-06-01), None
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patent: 63-288987 (1988-11-01), None
patent: 63-295494 (1988-12-01), None
pa
Aydelott Richard M.
Groat Clifford W.
Hiteshew Felisa
Oliff & Berridg,e PLC
SEH-America, Inc.
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