Patent Application
20090183670
The present invention relates to an apparatus for manufacturing a semiconductor single crystal ingot and a method using the same, and in particular to an apparatus for manufacturing a semiconductor single crystal ingot that provides a large and uniform temperature gradient in a radial direction of a solid-liquid interface in the manufacture of the semiconductor single crystal ingot by a Czochralski (hereinafter abbreviated to CZ) method, in particular, increases a temperature gradient of a center area of the solid-liquid interface, and a method using the same.
The CZ method is widely used to manufacture a semiconductor single crystal ingot, and grows a semiconductor single crystal ingot from a silicon melt in a quartz crucible. The CZ method uses a heater installed around a side wall of the quartz crucible to heat the silicon melt, and consequently, a natural convection is generated in the silicon melt. And, the CZ method manufactures a high-quality silicon single crystal free of grown-in defects generated from vacancy or self-interstitial by controlling a rotation rate of the single crystal or the quartz crucible, and consequently a forced convection is also generated in the silicon melt due to the control of rotation rate. It is well known that the natural and forced convection can be controlled by a horizontal magnetic field.
A method for applying a horizontal magnetic field to a silicon melt is referred to as a HMCZ (Horizontal Magnetic field CZochralski) method. A typical HMCZ method forms a magnetic field such that MGP (Maximum Gauss Plane) is located near the surface of a silicon melt. The MGP is a plane where a vertical component of a magnetic field is substantially close to ‘0’, and a flux density of the magnetic field in a horizontal direction becomes maximum. The horizontal magnetic field has characteristics that the vertical component of the magnetic field becomes ‘0’ at a central axis of a silicon single crystal. The HMCZ method using a horizontal magnetic field may suppress a vertical convection in a silicon melt and provides an advantage of easily growing a silicon single crystal.
Meanwhile, interstitial oxygen in a silicon wafer is used in various ways to manufacture a highly integrated semiconductor device. For example, the interstitial oxygen improves a mechanical strength of the silicon wafer to make the silicon wafer resistant against thermal stress generated during the manufacturing process of the device, and precipitates into micro-defects that serve as a gettering site to remove heavy metal impurities during the manufacturing process of the device.
The typical HMCZ method has an advantage of easily growing a single crystal ingot, but induces a change of an interstitial oxygen concentration in axial and radial directions of the ingot, resulting in production yield reduction of the ingot. This is because the locations of a high temperature area and a low temperature area on the surface of a silicon melt are changed due to an asymmetrical convection distribution of the silicon melt, so that an oxygen concentration distribution of a solid-liquid interface is not uniformly maintained. Here, the high temperature area is an area on the surface of the silicon melt having relatively higher temperature, and the low temperature area is an area on the surface of the silicon melt having relatively lower temperature.
To solve the above-mentioned problem, Korean Laid-open Patent Publication No. 2001-34851 discloses a method for manufacturing a silicon single crystal that applies a horizontal magnetic field to a silicon melt such that a vertical/horizontal component ratio of the horizontal magnetic field is 0.3 to 0.5 at the center of a solid-liquid interface to constantly maintain a high temperature area or a low temperature area having a uniform oxygen concentration at the solid-liquid interface, so that uniformity of oxygen concentration is improved in axial and radial directions of the single crystal.
However, since a non-linear forced convection is generated by rotation of a single crystal and a quartz crucible during growth of a silicon single crystal, it is difficult to fix the locations of a high temperature area and a low temperature area on the surface of a silicon melt throughout the single crystal growing process by controlling only a vertical/horizontal component ratio of a horizontal magnetic field. That is, simply controlling a vertical/horizontal component ratio of a horizontal magnetic field can not fundamentally prevent mixing of a high temperature area and a low temperature area or change in locations of the high temperature area and the low temperature area.
And, the Korean Laid-open Patent Publication No. 2001-34851 specifies a method for reducing a deviation of oxygen concentration in an axial or radial direction of a silicon single crystal, but does not mention a method to grow a high-quality silicon single crystal without grown-in crystal defects, at a rapid growing speed.
The present invention is designed to solve the above-mentioned problems. Therefore, it is an object of the present invention to provide an apparatus that controls distribution and density of a horizontal magnetic field to manufacture a high-quality semiconductor single crystal, and a method using the same.
It is another object of the present invention to provide an apparatus that controls distribution and density of a horizontal magnetic field to maximize the heat flow toward a solid-liquid interface from a heater, so that a temperature gradient of a center portion of the solid-liquid interface is increased to improve a pulling speed of a defect-free single crystal, and a method using the same.
It is yet another object of the present invention to provide an apparatus that controls distribution and density of a horizontal magnetic field to expand a processing margin of a defect-free pulling speed.
In order to achieve the objects of the present invention, the present invention provides an apparatus for manufacturing a semiconductor single crystal ingot including: a quartz crucible for receiving a semiconductor melt; a heater installed around a side wall of the quartz crucible; a single crystal pulling means for pulling a single crystal from the semiconductor melt received in the quartz crucible; and a magnetic field applying means for forming a Maximum Gauss Plane (MGP) at a location of ML-100 mm to ML-350 mm based on a Melt Level (ML) of the melt surface, and applying a strong magnetic field of 3000 to 5500 Gauss to an intersection between the MGP and the side wall of the quartz crucible and a weak magnetic field of 1500 to 3000 Gauss below a solid-liquid interface.
In order to achieve the objects of the present invention, the present invention provides a method for manufacturing a semiconductor single crystal ingot that pulls a semiconductor single crystal from a semiconductor melt received in a quartz crucible by a Czochralski process, including applying a horizontal magnetic field to the semiconductor melt during growth of the semiconductor single crystal by forming a Maximum Gauss Plane (MGP) at a location of ML-100 mm to ML-350 mm based on a Melt Level (ML) of the melt surface, and applying a strong magnetic field of 3000 to 5500 Gauss to an intersection between the MGP and a side wall of the quartz crucible and a weak magnetic field of 1500 to 3000 Gauss below a solid-liquid interface.
The magnetic field applying means includes at least one coil pair installed at opposite sides around the quartz crucible. The direction of current applied to each coil of the magnetic field applying means is determined by an electromagnetic law to meet the above-mentioned magnetic field forming conditions.
The horizontal magnetic field may be formed by controlling radius, location or shape of each coil of the magnetic field applying means, or direction and magnitude of current applied to the each coil.
The MGP intersection is approximately consistent with a side wall area of the quartz crucible heated to a highest temperature by heat emitted from a heater. Accordingly, in case that a strong magnetic field is formed at the MGP intersection, an amount of heat flux provided below the solid-liquid interface is increased. And, in case that a weak magnetic field is formed below the solid-liquid interface, the heat flux provided by the heater is effectively transferred to the solid-liquid interface to increase a temperature gradient of the solid-liquid interface, in particular a temperature gradient of a center portion of the solid-liquid interface.
The present invention will be more fully described in the following detailed description, taken accompanying drawings, however, the description proposed herein is just a preferable example for the purpose of illustrations, not intended to limit the scope of the invention.
a and 2b are views illustrating coil arrangement structures of a magnetic field applying means.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention.
Referring to
The above-mentioned components are typical components of a well-known apparatus for manufacturing a semiconductor single crystal by a CZ method, and the detailed description of each component is omitted. The semiconductor melt (M) may be a silicon melt obtained by melting a polycrystalline silicon, however the present invention is not limited to a specific kind of semiconductor melt. Therefore, the present invention can be applied to any semiconductor single crystal that is known to grow by a CZ method.
The apparatus for manufacturing a semiconductor single crystal ingot according to the present invention further includes a magnetic field applying means 80 for applying a horizontal magnetic field. Here, the horizontal magnetic field is a magnetic field, of which a vertical component of a magnetic field passing through a central axis of a single crystal ingot is substantially ‘0’.
In
The magnetic field applying means 80 has 2n coils (n is an integer larger than 0) that are arranged symmetrically relative to the quartz crucible 10. The coil has an approximate ring shape, and a normal direction of a plane of the coil is arranged perpendicularly to an outer wall of the insulating means 50. For example, as shown in
Preferably, the magnetic field applying means 80 forms a weak magnetic field below the solid-liquid interface where a semiconductor single crystal is grown, and a strong magnetic field at an intersection (hereinafter referred to as an ‘MGP intersection’) between the MGP and the side wall of the quartz crucible 10. Here, the weak magnetic field is formed directly below the solid-liquid interface. And, the weak magnetic field is a magnetic field having an intensity of about 1500 to 3000 Gauss, and the strong magnetic field is a magnetic field having an intensity of about 3000 to 5500 Gauss. The intensity conditions of the magnetic field are selected for the purpose of increasing a temperature gradient of a center portion of the solid-liquid interface. Here, unless otherwise specified, the temperature gradient is a vertical temperature gradient of the solid-liquid interface in the direction of single crystal. Meanwhile, preferably the MGP is located at ML-100 mm to ML-350 mm based on ML (Melt Level) that is a height of the melt surface measured at the center of the solid-liquid interface. The location conditions of the MGP are selected for the purpose of increasing an amount of heat flux provided from the heater 40 to the solid-liquid interface to the maximum extent. The location of the MGP is approximately consistent with an area of the side wall of the quartz crucible 10 where a largest temperature increase occurs due to heat emitted from the heater 40. In a high temperature silicon melt region near the side wall of the quartz crucible 10 heated by the heater 40, a natural convection is suppressed by the strong magnetic field and the flow of the high temperature silicon melt is promoted along the lines of horizontal magnetic force, so that heat is effectively transferred below the solid-liquid interface. The heat transferred below the solid-liquid interface can be actively transmitted vertically to the solid-liquid interface in the weak magnetic field area.
The horizontal magnetic field may be formed by controlling location of each coil, direction of current applied to the each coil or intensity of a magnetic field generated from the each coil. Alternatively, weak and strong magnetic fields may be formed below the solid-liquid interface and at the MGP intersection, respectively, by controlling radius of each coil. That is, as the radius of the coil is reduced, the magnetic field of the MGP intersection becomes stronger and the magnetic field below the solid-liquid interface becomes weaker. Further alternatively, weak and strong magnetic fields may be formed below the solid-liquid interface and at the MGP intersection, respectively, by changing the shape of a ring-shaped coil. For example, as the shape of the coil is changed by reducing a curvature of an upper part of the coil rather than a lower part of the coil, the magnetic field of the MGP intersection becomes stronger and the magnetic field below the solid-liquid interface becomes weaker. Still further alternatively, weak and strong magnetic fields may be formed below the solid-liquid interface and at the MGP intersection, respectively, by shielding a magnetic field generated from an upper part of the coil. It is obvious to ordinary persons skilled in the art that the above-mentioned methods for forming a magnetic field may be used in combination or singularly.
When the horizontal magnetic field is applied to the semiconductor melt (M) according to the present invention, an amount of heat flux flowing from the heater 40 to the solid-liquid interface is increased. Because a strong magnetic field is formed at the MGP intersection, convection of the semiconductor melt (M) is suppressed in an area of the quartz crucible 10 having a highest temperature, and consequently an amount of heat transmitted below the solid-liquid interface is increased. And, because a weak magnetic field is formed below the solid-liquid interface, heat transmitted from the heater 40 by the heat flux is actively transmitted to the solid-liquid interface. As a result, a temperature gradient of the solid-liquid interface, in particular a temperature gradient of a center portion of the solid-liquid interface is increased, thereby improving a pulling speed of a defect-free single crystal.
Meanwhile, according to the Voronkov's theory related to growth of a semiconductor single crystal, a processing margin of a pulling speed for growing a defect-free semiconductor single crystal ingot is closely related with a deviation of temperature gradient of the solid-liquid interface in a radial direction. That is, as a deviation of temperature gradient between a center portion of the solid-liquid interface and an edge portion of the solid-liquid interface becomes smaller, a processing margin of a pulling speed is increased. The present invention can increase a temperature gradient of a center portion of a solid-liquid interface that is difficult to control, by use of a horizontal magnetic field, and therefore, controls a temperature of an edge portion of the solid-liquid interface by controlling a melt-gap, which is a gap between the heat shield means 70 and the semiconductor melt (M), to reduce a deviation of temperature gradient of the solid-liquid interface in a radial direction, thereby easily expanding a processing margin of a pulling speed.
Hereinafter, a method for manufacturing a silicon single crystal ingot using the apparatus according to the present invention is described.
First, polycrystalline silicon is charged into the quartz crucible 10 in accordance with desired conditions of a silicon single crystal ingot to be manufactured. Next, the heater 40 is operated to melt the polycrystalline silicon. After the polycrystalline silicon is melted, the quartz crucible 10 is rotated in a predetermined direction by the crucible rotating means 30. After a predetermined time passes, convection of the silicon melt (M) is stabilized, and then the single crystal pulling means 60 is controlled to dip a seed crystal into the silicon melt (M) and pull up the seed crystal while slowly rotating the seed crystal. In this way, a silicon single crystal ingot is grown. At an early stage of growth, a pulling speed of the seed crystal is controlled such that diameter of the single crystal is increased to a desired diameter and thus a shoulder of the ingot is formed. After the shoulder is formed, a body of the ingot is grown at a defect-free pulling speed while maintaining the diameter of the body. After the body is grown, the pulling speed is increased such that a lower end of the ingot comes out of the silicon melt (M) while slowly reducing the diameter of the ingot. Thereby, growth of the ingot is completed.
During growth of the ingot, a horizontal magnetic field is applied to the silicon melt (M) by the magnetic field applying means 80. The horizontal magnetic field forms a weak magnetic field below the solid-liquid interface and a strong magnetic field at the MGP intersection. Applying the horizontal magnetic field according to the above-mentioned conditions increases an amount of heat flux from the heater 40 toward the solid-liquid interface, thereby increasing a temperature gradient of the solid-liquid interface, in particular a temperature gradient of a center portion of the solid-liquid interface. And, while the horizontal magnetic field is applied, the melt-gap between the heat shield means 70 and the silicon melt (M) is controlled to increase a temperature gradient of an edge portion of the solid-liquid interface, thereby removing a deviation in temperature gradient between a center portion of the solid-liquid interface and the edge portion of the solid-liquid interface. Applying the horizontal magnetic field and controlling the melt-gap according to the invention, the temperature gradient of the solid-liquid interface is increased on an overall area of the solid-liquid interface to improve a defect-free pulling speed, and the deviation in temperature gradient between the center portion and the edge portion of the solid-liquid interface is reduced to expand a processing margin of a defect-free pulling speed.
Hereinafter, the present invention is described in more detail through experimental examples. It should be interpreted that the experimental examples are given to help understand the present invention and the present invention is not limited to terms or conditions of the experimental examples.
A silicon single crystal ingot was grown by optimizing a hot zone and setting a melt-gap to 50 mm so that a defect-free pulling speed margin is obtained between an upper pulling speed and a lower pulling speed while changing a pulling speed. The pulling speed was gradually reduced from an early stage of growth to a later stage. During growth of the ingot, a horizontal magnetic field was applied to form a magnetic field of 3300 Gauss below a solid-liquid interface and a magnetic field of 4000 Gauss at an MGP intersection. The horizontal magnetic field was formed by arranging two coils as shown in
After the ingot was grown, the ingot was cut in an axial direction and evaluated through a vertical sampling inspection.
A silicon single crystal ingot was grown under the same conditions as the comparative example 1 except that a melt-gap was set to 40 mm, and gone through a vertical sampling inspection.
A radius of the coil used in the comparative example was reduced to 70%, and a melt-gap was set to 40 mm.
A horizontal magnetic field was formed by arranging two coils as shown in
A horizontal magnetic field was formed by arranging four coils as shown in
The following table shows the measurement results obtained from comparative examples 1 and 2 and examples 1 to 3.
Referring to Table 1, it is found that in single crystal growth by a CZ method, a horizontal magnetic field is applied to form a weak magnetic field below a solid-liquid interface and a strong magnetic field at an MGP intersection, thereby increasing a pulling speed of a defect-free single crystal and expanding a processing margin of a defect-free pulling speed.
According to an aspect of the present invention, the present invention effectively transmits heat emitted from the heater toward a region below the solid-liquid interface where a single crystal is grown, thereby improving a pulling speed of a defect-free single crystal. Consequently, the present invention can improve productivity of a defect-free single crystal ingot.
According to another aspect of the present invention, the present invention improves a temperature gradient of the solid-liquid interface, and at the same time, controls a melt-gap capable of controlling a temperature gradient of an edge portion of a single crystal, thereby expanding a processing margin of a defect-free pulling speed.
According to yet another aspect of the present invention, the present invention actively transmits heat emitted from the heater toward a region below the solid-liquid interface, where a single crystal is grown, thereby reducing a heating power of the heater, resulting in reduction of energy needed to operate the heater.
Hereinabove, preferred embodiments of the present invention has been described in detail with reference to the accompanying drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2008-0006307 | Jan 2008 | KR | national |
