JPH06340490A - Apparatus for production of silicon single crystal - Google Patents

Abstract

PURPOSE:To provide the apparatus for production of a silicon single crystal having the excellent pressure resistance of an oxidized film which improves a heat history by adjusting the temp. gradient of the silicon single crystal during pulling up. CONSTITUTION:This apparatus for production of the silicon single crystal has an inverted circular cone-shaped shielding member 8 which is disposed around a single crystal pulling-up region above the melt 7 in a crucible and is reduced in diameter toward the lower side from the upper side and a cylindrical shielding member 10 which is in tight contact with the top end of this member 8, has the bore nearly coinciding with the outside diameter thereof and is disposed coaxially with the member 8. Further, a heat insulating material 9 is sealed into the member 8 and the outer periphery of the member 10 is coated with a heat insulating material 11. The member 8 and member 10 are made of graphite. The heat insulating material 9 and heat insulating material 11 are made of carbon fibers. The thickness of the heat insulating material 9 is preferably <=10mm and the thickness of the heat insulating material 11 >=10mm. The thickness of the latter is preferably <=10mm and the thickness of the heat insulating material 11 >=10mm. The thickness of the latter is preferably >=2.0 times the thickness of the former.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a silicon single crystal, and more particularly to an apparatus for producing a silicon single crystal having excellent oxide film withstand voltage characteristics.

[0002]

2. Description of the Related Art There are various methods for producing a single crystal. Among them, the Czochralski method is widely used as a method for industrially mass-producing a silicon single crystal.

FIG. 5 is a vertical cross-sectional view showing an implementation state of the Czochralski method, in which 2 is a crucible. A heating heater 3 and a heat insulating material 4 are provided outside the crucible 2, and the crucible 2 contains a crystal forming material melted by the heating heater, that is, a raw material melt 7. The lower end of a seed crystal 5 attached to the tip of a pulling rod or a wire is brought into contact with the surface of the melt 7 and the seed crystal 5 is pulled upward to grow a single crystal 6 in which the melt 7 is solidified. I will let you. These parts and members are housed in a water-cooled metal chamber 1 and constitute a silicon single crystal manufacturing apparatus as a whole.

In mass production of a single crystal, the pulling rate largely depends on the temperature gradient in the pulling direction of the crystal. Here, the temperature gradient is a rate at which the pulled crystal is cooled, and represents a temperature difference (° C.) at which the crystal is cooled per unit length (1 cm) of the crystal. Average temperature gradient from the start of cooling to the end of cooling (° C
/ cm). Therefore, in order to increase the pulling rate, it is necessary to increase the cooling rate, that is, the temperature gradient of the crystal. However, in the apparatus shown in FIG. 5, there are radiant heat sources such as the crucible 2, the heater 3 and the melt 7 around the single crystal 6, and the radiant heat received from these is large, so the temperature gradient in the pulling direction of the crystal is small. I was unable to increase the pulling speed.

Further, during the pulling of the single crystal 6, a high-purity argon gas is constantly supplied into the metal chamber 1. This is silicon monoxide (Si) that evaporates from the surface of the silicon melt 7.
This is because the gas is discharged together with O) from a discharge port (not shown) below. However, the flow of the argon gas in the metal chamber 1 is a complicated turbulent flow, and since the residence also locally occurs, the deposits of silicon monoxide adhere to the ceiling of the metal chamber 1 in a layered or lumpy manner. Often, fine particles or lumps of silicon monoxide fall on the surface of the melt 5.

This may be taken into the crystal growth interface, causing dislocation-free crystals to have dislocations, resulting in a defective single crystal.

As a measure for increasing the pulling rate and growing dislocation-free crystals, the following device has been conventionally proposed.

FIG. 2 shows an apparatus proposed by Japanese Examined Patent Publication No. 57-40119. This device consists of an upper flat annular rim 8a projecting from the crucible edge and a connecting part 8b attached to this annular rim 8a and conically tapering downward from the inner edge. It is characterized in that a member whose internal height of the connecting portion 8b is 0.2 to 1.2 times the depth of the crucible 1 is provided.

FIG. 3 shows an apparatus disclosed in Japanese Patent Laid-Open No. 63-256593, which is a cylindrical metal shielding member 8 whose diameter is reduced from the upper side to the lower side, and the metal shielding member 8 And a cylindrical shielding member 9 disposed outside the metal shielding member 8 with a required gap to shield the outer peripheral surface of the metallic shielding member 8 from the evaporation material from the molten liquid and the radiant heat source.
It is characterized by having and.

The above-mentioned conventional apparatus has a certain effect in preventing the dropping of fine particles of silicon monoxide into the silicon melt and improving the crystal pulling rate by the radiation heat shielding effect.

[0011]

In recent years, as the integration density of MOS devices has increased, various characteristics have been required for a silicon wafer processed after pulling a single crystal. Especially DR
As the integrated circuit of AM becomes finer, the gate oxide film becomes thinner, and under a constant power supply voltage, the applied electric field strength applied as stress to the gate oxide film is high. Reliability is strongly desired. Since the oxide film breakdown voltage is one of the important material properties that determine its reliability, there is an urgent need to develop a single crystal having excellent oxide film breakdown voltage characteristics and a manufacturing technique therefor. However, the above-mentioned conventional device has a problem in manufacturing a single crystal having excellent oxide film withstand voltage characteristics.

The details of the mechanism of forming a defect that deteriorates the oxide film withstand voltage characteristic are still unknown. However, although the oxide film breakdown voltage characteristic strongly depends on the crystal growth rate, it is due not to the crystal pulling rate itself but to the resulting thermal history during crystal growth. That is, during crystal growth due to pulling, defect nuclei that cause defects in the oxide film breakdown voltage characteristics are generated in the crystal, but these defect nuclei shrink in the high temperature region (1250 ° C or higher) and in the low temperature region (1100 ° C or lower). There is a report that it will grow (see the 39th Spring Applied Physics Society Proceedings, 30P-ZD-17).

In the apparatus shown in FIG. 2, since the internal height of the frustoconical cylindrical connecting portion 8b arranged around the pulled crystal is as low as 0.2 to 1.2 times the depth of the crucible, the crystal in the pulling process is Since it is exposed directly to the atmosphere inside the metal chamber that is kept at a low temperature from the time when it exceeds the connecting portion 8b, the cooling effect of the pulled crystal is increased and it is rapidly cooled while it is still in the high temperature region, and the defect nucleus is contracted. Since the single crystal grows without causing the breakdown voltage characteristic of the oxide film to deteriorate.

On the other hand, in the apparatus shown in FIG. 3, since the metallic shielding member 8 is provided with the cooling means 8a such as the cooling water pipe,
Although the temperature gradient of the crystal becomes large and the pulling rate becomes faster, the pulled crystal is rapidly cooled in a high temperature region, and the oxide film withstand voltage characteristic deteriorates.

Therefore, the conventional single crystal production apparatus has a problem that it cannot be applied to the production of a silicon single crystal excellent in the oxide film withstand voltage characteristic required as the MOS device integration degree increases as described above. Was there. In view of this problem, the present invention aims to provide an apparatus for manufacturing a silicon single crystal having excellent oxide film withstand voltage characteristics by adjusting the temperature gradient of the crystal and improving the thermal history of the silicon single crystal. To do.

[0016]

DISCLOSURE OF THE INVENTION The gist of the present invention is, for example, the following silicon single crystal manufacturing apparatus as shown in FIG.

A crucible 2 for containing a melt of a single crystal to be grown, a means 3 for heating the melt, and a pulling means 5 for growing a single crystal by bringing a seed crystal into contact with the surface of the melt in the crucible. A single crystal manufacturing apparatus comprising a metal chamber 1 for accommodating the above-mentioned members, wherein the diameter is reduced from the upper side to the lower side provided around the single crystal pulling region above the melt 7 in the crucible. The inverted conical shielding member 8 and a cylindrical shield that is in close contact with the upper end of the inverse conical shielding member 8 and has an inner diameter that substantially matches the outer diameter of the conical shielding member 8 and is coaxially arranged with the inverse conical shielding member 8. And a heat insulating material 9 is enclosed inside the inverted conical shielding member 8 and a heat insulating material 11 is coated on the outer periphery of the cylindrical shielding member 10. Single crystal manufacturing equipment.

The inverse conical shielding member 8 and the cylindrical shielding member 10 are made of graphite, and the heat insulating material 9 enclosed in the inverse conical shielding member and the heat insulating material 11 coated on the outer periphery of the cylindrical shielding member are provided. It is preferably made of carbon fiber. In addition, the thickness of the former heat insulating material 9 is 10 mm or less, and the thickness of the latter heat insulating material 11 is
It is desirable that the thickness of the heat insulating material of 10 mm or more and the latter is 2.0 times or more the thickness of the former.

[0019]

In order to complete a silicon single crystal manufacturing apparatus having excellent oxide film withstand voltage characteristics, the present inventor has studied in detail the means for adjusting the thermal history and temperature gradient of the single crystal during crystal growth by pulling the crystal. As a result, we obtained the following findings.

Providing a thermal history of gradual cooling in the high temperature region where the defect nuclei shrink and disappear reduces the temperature gradient in the high temperature region (1250 ° C. or higher) when the crystal is cooled from the solidification temperature. It is possible if adjusted.

The temperature gradient in the crystal pulling direction is closely related to the surface temperature of the inverted conical shielding member.
That is, if the surface temperature of the inverted conical shielding member is low, the temperature gradient of the crystal is large, and if the surface temperature of the inverse conical shielding member is high, the temperature gradient of the crystal is small.

In order to keep the surface temperature of the inverted conical shielding member at a high temperature, it is effective to provide a cylindrical shielding member that surrounds the inverted conical shielding member from the outer circumference. This is because the cylindrical shielding member can reduce heat emission due to radiant heat transfer to the water-cooled metal chamber.

Further, in order to reduce the heat release due to the radiant heat transfer, it is more effective to coat the outer circumference of the cylindrical shielding member with a heat insulating material. In this case, the surface temperature of the inverted conical shielding member is maintained at a high temperature.For example, when a graphite inverted conical shielding member with high thermal conductivity is used, the temperature becomes extremely high, and the temperature is raised more than necessary. It will slow down. Therefore, in order to adjust the temperature gradient of the crystal while maintaining a predetermined pulling rate, it is effective to insert a heat insulating material into the inverted conical shielding member.

Further, by keeping the surface temperature of the inverted conical shielding member at a high temperature, it is possible to suppress the deposition of silicon monoxide vaporized from the silicon melt on the outer peripheral surface of the inverted conical shielding member, and It is possible to prevent fine powder or lumps that are precipitates of silicon from falling onto the surface of the melt.

The present invention has been completed based on the above findings. Hereinafter, the silicon single crystal production apparatus of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a vertical sectional view showing the device of the present invention. In the figure, 2 is a crucible, which is installed on the crucible support shaft 2a. The crucible support shaft 2a is adapted not only to rotate the crucible but also to elevate and lower the crucible.

In the figure, reference numeral 1 shows a water-cooled metal chamber. The metal chamber 1 is a cylindrical vacuum container centered on a pulling axis of a single crystal, and a crucible 2 is arranged at the center position thereof. A heater 3 and a heat insulating material 4 are provided around the outer periphery of the crucible 2 so as to surround it. On the other hand, crucible 2
A pulling shaft is hung from above the center of the ceiling of the metal chamber 1 so as to be rotatable and movable up and down, and a seed crystal 5 is attached to the lower end of the pulling shaft. The seed crystal 5 rises while rotating as the pulling shaft rotates, and the pulling crystal 6 grows at the lower end portion which is a contact surface with the melt 7.

One of the features of the device of the present invention is that an inverted conical shielding member 8 is arranged coaxially with the pulling shaft around the pulling region of the single crystal 6 above the melt 7 in the crucible 2. Is.

This shape is an inverted conical cylinder whose diameter is reduced from the upper side to the lower side. Further, another feature of the device of the present invention is that the cylindrical shielding member 10 which is in close contact with the upper end of the inverted conical shielding member 8 and has an inner diameter substantially matching the outer diameter thereof is
That is, it is provided coaxially with the inverted conical shielding member 8. The thickness of the cylindrical shielding member 10 may be about 10 mm.

It is desirable that the inverted conical shielding member 8 and the cylindrical shielding member 10 are made of graphite. Since the temperature of the pulling region becomes a high temperature of about 1500 ° C. due to radiant heat, it is desirable to use graphite that has high high-temperature strength, high purity, and is free from the risk of contamination of the pulling crystals by the contained heavy metal.

The inverted conical shielding member 8 has a double structure,
The entire thickness is about 5 mm to 20 mm, and a heat insulating material 9 having substantially the same shape as the inverted conical shielding member 8 is enclosed inside. The heat insulating material 9 is enclosed in order to properly adjust the temperature gradient of the crystal. The surface temperature of the inverted conical shielding member 8 that does not enclose the heat insulating material 9 becomes high, and the temperature gradient of the crystal becomes extremely small. According to the experiment conducted by the inventor, the thickness of the heat insulating material 9 is preferably in the range of 2 mm to 10 mm in order to secure the pulling rate and to grow a single crystal having an excellent oxide film withstand voltage characteristic.

Further, the outer circumference of the cylindrical shielding member 10 is covered with a heat insulating material 11. The thickness of the heat insulating material 11 is more effective as it is thicker in order to reduce heat emission due to radiative heat transfer to the water-cooled metal chamber, but it is practically 10 mm.
~ 100 mm is sufficient. Further, the thickness of the heat insulating material 11 is preferably 2.0 times or more the thickness of the heat insulating material 9. Although the theoretical basis for this reason cannot be found yet, according to the experimental results, when the thickness of the heat insulating material 11 is 2.0 times or less than the thickness of the heat insulating material 9, the temperature gradient in the high temperature region and the low temperature region becomes large. This is because it becomes larger.

Further, it is preferable that the heat insulating material 9 and the heat insulating material 11 are made of carbon fiber. This is because carbon fiber has a sufficiently small thermal conductivity and a high-purity material can be manufactured. This is because the pulled crystal can be prevented from being contaminated with heavy metals while being ensured.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the silicon single crystal production apparatus of the present invention will be described below with reference to the drawings.

In the manufacturing apparatus of the present invention shown in FIG. 1, the inverted conical shielding member 8 has dimensions of 10 mm in thickness and 380 mm in height,
The inner diameter of the upper end was 400 mm and the inner diameter of the lower end was 200 mm, and the thickness of the heat insulating material 9 enclosed in this was 5 mm. Cylindrical shielding member 10
Has a thickness of 10 mm and is in close contact with the outer diameter of the upper end portion of the inverted conical shielding member 8, and its inner diameter matches the outer diameter of the upper end portion of the inverted conical shielding member 8. The thickness of the heat insulating material 11 covering the cylindrical shielding member 10 is set to 10 mm, and the ratio of the thickness of this heat insulating material 11 to the thickness of the heat insulating material 9 (thickness of the heat insulating material 11 / thickness of the heat insulating material 9)
Is set to 2.0.

The single crystal 6 to be pulled is a silicon single crystal having a diameter of 6 inches, the crucible 2 has an inner diameter of 457 mm (18 inches), and the crucible 2 is a solid raw material for crystal formation. -Shaped or granular polycrystalline silicon
It was filled with 50 kg. The flow rate of argon gas flowing into the metal chamber 1 was 60 liters / min, and the pulling rate was 1.0 mm / m.
in, the pulling length was 1000 mm.

Further, as an embodiment of the present invention, the ratio of the thickness of the heat insulating material 11 to the thickness of the heat insulating material 9 (the thickness of the heat insulating material 11 / the heat insulating material 9
Thickness) was set to 4.0 and 1.25, and for comparison with the examples of the present invention, the pulling was performed under the conditions summarized in Table 1 as Comparative Examples 4 to 6.

FIG. 4 is a view in which the thermocouple 12 is inserted in the single crystal 6. The temperature gradient of the crystal during pulling was measured by this thermocouple 12. Table 1 shows the measurement results of the temperature gradient in the high temperature region (around 1300 ° C) and the low temperature region (around 1100 ° C) at that time.
Shown in.

[0039]

[Table 1]

From Table 1, the temperature gradient of the single crystal pulled under the conditions of the shielding member and the heat insulating material of the present invention is smaller than that of the comparative example, especially in a high temperature region.

However, when the ratio of the thickness of the heat insulating material 11 to the thickness of the heat insulating material 9 is 2.0 or less, the temperature gradient of the single crystal becomes slightly large.

In order to evaluate the oxide film breakdown voltage characteristics, the 6-inch silicon single crystal pulled up by the present manufacturing apparatus was subjected to processing necessary for industrially manufacturing a normal silicon wafer such as slicing and polishing. After covering the surface of the silicon wafer with an oxide film, a gate electrode was formed. The oxide film was coated by a thermal oxidation method in which a heat treatment was performed in an oxidizing atmosphere, and a dry oxide film having a film thickness of 25 nm was used. The gate electrode is made of phosphorus (P) -doped polycrystalline silicon and has an area of 8 mm ² .

The evaluation of the oxide film breakdown voltage characteristic of this silicon wafer is based on the voltage ramping method which is an electrical evaluation method of the oxide film. In this method, the applied voltage is increased in every 1v step on the silicon wafer forming the gate electrode,
The leak current is measured.

Usually, 100 to 150 measurement points are provided on the surface of the silicon wafer, and the evaluation is performed by the dielectric breakdown judgment of each oxide film and the quality judgment of the silicon wafer. In the dielectric breakdown judgment of the oxide film, the dielectric breakdown is judged when the leak current density of 12.5 μA / cm ² or more is measured.

Further, the quality of the silicon wafer is judged to be defective at the measurement point where the dielectric breakdown occurs at an average electric field of 8 Mv / cm or less, and the ratio of non-defective parts on the wafer surface represents the non-defective product rate. In general, the evaluation of oxide film withstand voltage characteristics depends on the yield rate of silicon wafers.

The measurement results of the yield rate of the above silicon wafers are shown in Table 2. In order to clarify the comparison of the measurement results,
In the apparatus of the present invention, the non-defective rate of the single crystal silicon wafer manufactured under the conditions of Inventive Example 1 in which the thickness ratio of the heat insulating material 11 and the thickness of the heat insulating material 9 is 2.0 is represented as 1.0.

[0047]

[Table 2]

From Table 2, the non-defective rate is low in each of the comparative examples, but the non-defective rate is high in the single crystal pulled under the conditions of the shielding member and the heat insulating material of the present invention example.
However, among the examples of the present invention, No. 3 has a slightly low yield rate. Therefore, it is desirable that the thickness of the heat insulating material coated on the outer periphery of the cylindrical shielding member is 2.0 times or more the thickness of the heat insulating material enclosed in the inverted conical shielding member.

Further, in any of the single crystals pulled by the production apparatus of the present invention, the problem of dislocation generation due to the precipitate of silicon monoxide did not occur.

[0050]

The single crystal production apparatus of the present invention has a simple structure and is easy to handle, and can appropriately control the temperature gradient in the pulling direction of the single crystal. According to the device of the present invention, it is possible to improve the withstand voltage characteristic of an oxide film of a single crystal substrate and prevent dislocation due to a precipitate of silicon monoxide without lowering the productivity of the single crystal.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a silicon single crystal production apparatus of the present invention.

FIG. 2 is a vertical sectional view showing an example of a conventional single crystal manufacturing apparatus.

FIG. 3 is a vertical cross-sectional view showing another example of a conventional single crystal manufacturing apparatus.

FIG. 4 is a diagram in which a thermocouple is inserted in a single crystal in order to measure the temperature gradient of the crystal during pulling.

FIG. 5 is a vertical cross-sectional view showing an implementation state of the Czochralski method.

[Explanation of symbols]

1 ... Metal chamber, 2 ... Crucible, 2a ... Crucible support shaft, 3
... Heater 4 ... Insulating material, 5 ... Seed crystal, 6 ... Single crystal, 7 ... Melt liquid, 8
... Inverse conical shielding member 9, 11 ... Insulating material, 10 ... Cylindrical shielding member, 12 ... Thermocouple

Claims (2)

[Claims] 1. A crucible for containing a melt of a single crystal to be grown, a means for heating the melt, and a pulling means for bringing a seed crystal into contact with the surface of the melt in the crucible to grow the single crystal. A single crystal manufacturing apparatus comprising a metal chamber that accommodates each of the above-mentioned members, wherein the diameter of the melt is reduced in the reverse direction from the upper side to the lower side, which is arranged around the single crystal pulling region above the melt in the crucible. A conical shielding member, and a cylindrical shielding member that is in close contact with the upper end of the inverted conical shielding member, has an inner diameter that substantially matches its outer diameter, and is arranged coaxially with the inverse conical shielding member, Further, a heat insulating material is enclosed in the inside of the inverted conical shielding member, and an outer periphery of the cylindrical shielding member is covered with a heat insulating material. 2. The inverted conical shielding member and the cylindrical shielding member are made of graphite, and the heat insulating material enclosed in the inverse conical shielding member is made of carbon fiber, and the thickness thereof is 10 mm or less. The heat insulating material coated on the outer periphery of the cylindrical shielding member is also made of carbon fiber and has a thickness of 10 mm or more, and at least 2.0 times the thickness of the heat insulating material enclosed in the inverted conical shielding member. 2. It has a thickness of 1.
The described silicon single crystal manufacturing apparatus.