JP2004083389A - Silicon single crystal and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon single crystal and a method for producing the same in which even a large-diameter silicon single crystal can be separated without dislocation without harmful effect on crystal characteristics in a short time. <P>SOLUTION: The silicon single crystal produced by Czochralski method has a tail end surface in which an annular recessed part is formed along the periphery thereof; a disk raised section is concentrically formed inside the annular recessed part; and a protruding liquid droplet section is formed during separation facing downward at the center of the disk raised section. The silicon single crystal also has an inclined portion at the periphery of the tail end surface in which an annular recessed part is formed in the inner side thereof; a disk raised section is concentrically formed inside the annular recessed part; and a protruding liquid droplet section is formed during separation facing downward at the center of the disk raised section. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a silicon single crystal and a method for producing a silicon single crystal by a CZ method (Czochralski method).
[0002]
Further, the present invention relates to a manufacturing method for shortening or omitting the tail step when manufacturing a silicon single crystal by the CZ method.
[0003]
[Prior art]
In manufacturing a silicon single crystal used as a material of a semiconductor device, a CZ pulling method is often used. In this method, first, a silicon seed crystal is immersed in a raw material melt melted in a quartz crucible. Next, the silicon single crystal is grown under the quartz crucible and the seed crystal by pulling the seed crystal while rotating the seed crystal in the same direction or in the opposite direction. These usually consist of steps of neck, shoulder, body and tail.
[0004]
In the neck step, the crystal diameter is narrowed down to remove dislocations caused by thermal shock when the seed crystal is immersed in the raw material melt. In the shoulder process, the crystal diameter is expanded to a target diameter. In the body process, the growth is continued while maintaining the crystal at the target diameter. As a result, a cylindrical straight body is formed. In the last tail step, the crystal diameter is gradually reduced, and separated from the melt. Thus, an inverted conical tail portion is formed below the straight body portion. The tailing step is performed in order to prevent slipback (extending substantially upward by the crystal diameter) that occurs when the crystal is separated from the melt.
[0005]
Of the silicon single crystal, the neck, crown, shoulder, and tail are not used as products because their crystal diameters are less than a predetermined value or are not constant. It is the tail portion that takes the longest time to produce and among the parts that are not used as a product. Since the diameter of the crystal is gradually reduced in the tail step, the crystal diameter is not stable, and it is difficult to control the heater power and the pulling speed.
[0006]
Further, in recent years, due to an increase in diameter of a silicon single crystal, it tends to take a long time to prepare the tail.
[0007]
Methods for shortening or omitting the tail step by separating a silicon single crystal without dislocations are reported in Patent Documents 1, 2 and 3, and the like. In any case, it is considered that the cut end face of the silicon single crystal preferably has a downward convex shape.
[0008]
However, due to the recent increase in the diameter of the silicon single crystal, it is difficult to make the cut end face of the silicon single crystal completely convex downward. In the case of a small-diameter silicon single crystal, since the temperature difference between the central portion and the outer peripheral portion of the single crystal is small, by performing an operation such as dropping the pulling speed immediately before disconnection, the separated end surface can be made to have a downwardly convex shape, When the diameter of the pulled single crystal is 300 mm or more, the temperature difference between the central portion and the outer peripheral portion of the single crystal increases, and the outer peripheral portion having a relatively low temperature solidifies faster than the central portion having a higher temperature, and the cut end faces upward. It tends to be concave.
[0009]
[Patent Document 1]
JP-A-9-208376 [0010]
[Patent Document 2]
JP-A-9-208379
[Patent Document 3]
Japanese Patent Application Laid-Open No. H11-335197 discloses a method in which a silicon single crystal being pulled is once submerged in a melt to dissolve the outer peripheral portion of the single crystal. However, in this conventional method, once solidified crystals are dissolved, there is a high possibility of causing dislocations. In addition, if the pulling speed is reduced immediately before the separation and the outer peripheral portion of the single crystal is melted by sinking, the production takes a lot of time as the crystal diameter increases. In that case, the heat flow from the melt to the pulled single crystal adversely affects the characteristics.
[0012]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a silicon single crystal and a method for producing the same, which can be separated from a large-diameter silicon single crystal without dislocation in a short time without adversely affecting the crystal characteristics. .
[0013]
[Means for Solving the Problems]
An example of the solution of the present invention is as follows.
[0014]
(1) In a silicon single crystal manufactured by the Czochralski method, an annular concave portion is formed along an outer peripheral portion of a tail end surface of the silicon single crystal, and a disk is concentrically formed inside the annular concave portion. A silicon single crystal characterized by having a convex shape formed thereon, and a protruding droplet portion formed downward at the time of separation at the center of the disk-shaped convex portion.
[0015]
(2) In the silicon single crystal manufactured by the Czochralski method, the tail end face of the silicon single crystal has a slope at the outer periphery of the single crystal, and an annular concave portion is formed inside the slope. A disc-shaped convex portion is formed concentrically inside the annular concave portion, and a protruding droplet portion formed downward at the time of separation is formed at the center of the convex portion of the disk. A silicon single crystal characterized by the following.
[0016]
(3) The height difference from the uppermost part of the annular concave part to the lowermost part of the disk-shaped convex part excluding the liquid droplet part is 20 mm or less. The silicon single crystal according to 1.
[0017]
(4) The silicon single crystal according to any one of claims 1 to 3, wherein a diameter of the disk-shaped convex portion is larger than a width of the annular concave portion.
[0018]
(5) A method for producing a silicon single crystal by the Czochralski method, wherein when the silicon single crystal is separated from the raw material melt, the pulling speed is set to 0.2 mm / min. Below, and then the cutting speed is set to 200 mm / min. The method for producing a silicon single crystal according to claim 1, wherein:
[0019]
Method for manufacturing crystals.
[0020]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the first embodiment of the present invention, in improving the end face of the silicon single crystal manufactured by the Czochralski (CZ) method, the tail end face of the silicon single crystal has an annular concave portion along the outer peripheral portion. It is formed in an upwardly concave shape, and a disc-shaped convex portion is formed concentrically and continuously inside the annular concave portion so as to bulge downward. At the center of the disk-shaped projection, a projection-shaped droplet portion formed downward at the time of separation is formed.
[0021]
It is preferable that the diameter of the disk-shaped protrusion is larger than the width of the annular recess.
The height difference from the uppermost surface (highest portion) of the annular concave portion to the lowermost surface (lowest portion) of the disk-shaped convex portion excluding the droplet portion is preferably 20 mm or less.
As described above, according to the manufacturing method of the present invention, when the silicon single crystal is cut, the pulling speed is set to 0.2 mm / min. Below, and the cutting speed is 200 mm / min. As described above, it is assumed that there is no dislocation. In particular, the pulling time with the pulling speed reduced is set to 30 minutes or less.
[0022]
Normally, dislocations occur when a dislocation-free silicon single crystal is separated during pulling. As a cause, as shown in FIG. 1, the melt is lifted by being pulled by the solid crystal at the time of separation, and the melt portion solidifies from the outer peripheral portion, and finally the central portion solidifies, so that the melt occurs at that time. The volume expansion compresses the surrounding solid part and causes dislocation. Therefore, in order to prevent the occurrence of dislocations, it is necessary to suppress the amount of the melt lifted by the crystal at the time of separation. When the solid-liquid interface is largely convex upward as shown in FIG. 1, the melt is lifted up from the surrounding melt surface, and if it is cut at high speed in this state, a large amount of the melt will stick to the crystal. Therefore, by lowering the pulling speed just before the separation, the solid-liquid interface can be lowered, and the amount of the melt lifted at the time of the separation can be reduced as shown in FIG. Then, the thin film of the melt formed at that time is separated from the solid crystal and solidified toward the end face, and no pressure is applied to the solid crystal due to volume expansion, and no dislocation occurs.
[0023]
Another feature of the present invention is to improve the shape of the end face of a silicon single crystal manufactured by the Czochralski (CZ) method. Preferably, an inclined portion is provided on the outer peripheral portion of the tail end surface of the silicon single crystal, an annular concave portion is formed inside the inclined portion, and a disk-shaped concentric portion is formed inside the annular concave portion. A convex portion is formed, and a protruding droplet portion formed downward at the time of separation is formed at the center of the disk-shaped convex portion. Therefore, the outermost peripheral portion of the shape of the end face of the silicon single crystal is cut off as a shape inclined upward.
[0024]
Further, it is preferable that the diameter of the disk-shaped projection is larger than the width of the annular recess. Further, it is desirable that the height difference from the uppermost surface (highest portion) of the annular concave portion to the lowermost surface (lowest portion) of the disk-shaped convex portion excluding the droplet portion is 20 mm or less.
[0025]
In the above-described manufacturing method of the present invention, when the silicon single crystal is cut off, the pulling speed is set to 0.2 mm / min. The lifting speed in the state of being dropped below is 30 minutes or more, and the separation speed is 200 mm / min. Above. By doing so, the crystal having the above shape can be easily pulled up.
[0026]
By providing the inclined portion in the outer peripheral portion in this way, that is, by making the diameter go into the inside of the single crystal, the flow of solidification of the melt lifted at the time of cutting off the single crystal can be smoothly and uniformly performed in a uniform direction. And dislocation-free crystals can be easily obtained. Conversely, if the diameter increases at this point, the flow from the outside to the inside in the crystal diameter direction and the flow from the inside to the outside in the crystal diameter direction at the boundary of the outer periphery are likely to occur, and the progress of solidification is cut off and the end face becomes complicated It is considered that dislocation is likely to occur. Therefore, it is desirable to incline the outer peripheral portion inward.
[0027]
Patent Document 4 discloses a method of manufacturing a semiconductor single crystal by the CZ method, which is capable of preventing generation of dislocations in the body even if tail formation is omitted. Immediately after the completion of the process, the single crystal 8 is separated from the melt 2 by increasing the pulling speed (500 mm / min in the example), and thereafter, the pulling speed is controlled to gradually cool an arbitrary temperature region. The cooling is performed so that the cooling rate between the melting point and 1000 ° C. in the vicinity of the cut-off end face 8a is 35 ° C./min or less, or the cooling rate is 30 ° C. It is stated to hold for more than a minute.
[0028]
[Patent Document 4]
JP-A-9-307971 (FIG. 1)
However, the prior art of Patent Document 4 is characterized in that the single crystal is separated from the melt by raising the pulling speed (500 mm / min in the example) immediately after the growth of the single crystal body is completed. The phenomenon (the melt is lifted in the form of being pulled by the solid crystal at the time of separation) causes a variation in the amount of the lifted melt at the ends, and as a result, the separation end face is concave or concave as shown in this prior art. It is difficult to efficiently obtain an uneven single crystal ingot.
[0029]
Thus, the present invention provides a method for separating a silicon single crystal from a raw material melt, while adjusting the heater power and increasing the pulling rate to 0.2 mm / min. The speed at the time of separation after being lowered to 200 mm / min. The tail portion can be easily formed by raising and separating as described above. More preferably, the pulling speed is 0.2 mm / min. It is desirable that the continuation time when the temperature is reduced to 15 minutes or less is 15 minutes or less. Further, the crystal can be more smoothly separated from the melt by making the diameter of the crystal tend to decrease when the crystal is separated and making the outer periphery of the crystal bottom inwardly inclined as shown in FIGS. . As a manufacturing method at this time, when the silicon single crystal is separated from the raw material melt, the pulling rate is 0.2 mm / min. The continuation time at the time when the temperature was lowered to 30 minutes or less was set to 30 minutes or more, and the speed at the time of separation was set to 200 mm / min. It is characterized by the above. At this time, as shown in FIG. 3, the length d1 from the outermost periphery of the cut end face to the tip of the central projection is 1/1 / distance d2 (the distance from the outermost periphery of the cut end face to the surface of the raw material melt) held at the time of separation. It is preferably 2. Since the solidification of the pulled crystal is started from the crystal side toward the cut end face at the moment of separation from the melt, the cut needs to be performed instantaneously. When d1 is larger than 1/2 of d2, the pulled crystal remains connected to the raw material melt due to the surface tension of the raw material melt even when the separation is performed, and the separation cannot be performed instantaneously. For this reason, even if the heat from the raw material melt reaches the solidified portion and is re-melted, and then separated, the solidification flow is not separated from the solid crystal but at the end face and dislocations occur.
[0030]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0031]
FIG. 4 shows an example of a longitudinal sectional shape at the center of the tail end of the silicon single crystal according to the present invention.
[0032]
In FIG. 4, reference numeral 20 denotes a tail end of a silicon single crystal manufactured by the Czochralski (CZ) method. At the tail end portion 20 of the silicon single crystal, an annular concave portion 21 is formed along the outer peripheral portion, and a disk-shaped convex portion 22 is formed concentrically and continuously inside the annular concave portion 21. At the center of the disc-shaped convex portion 22, a protruding droplet portion 23 formed downward at the time of separation is formed.
When the diameter R of the tail end of the silicon single crystal is 286 to 325 mm, the depth a of the annular concave portion 21 is 10 mm or less (preferably 1 to 6 mm), and the height b of the disk-shaped convex portion 22 is b. (Excluding the droplet portion 23) is 15 mm or less (preferably 6 to 8 mm). The height difference c from the uppermost portion (the deepest portion) of the concave portion 21 to the lowermost portion (the highest portion) of the disk-shaped convex portion 22 excluding the droplet portion 23 is 20 mm or less.
[0033]
The diameter r of the disk-shaped projection 23 is larger than the width w of the annular recess 21. For example, the diameter r is preferably 160 to 180 mm, the width w is 65 to 85 mm, and the difference (r−w) between r and w is preferably 75 to 115 mm.
[0034]
FIG. 5 is a schematic cross-sectional view of a crystal growing apparatus for performing the single crystal manufacturing method according to the embodiment of the present invention.
[0035]
In FIG. 5, a crucible 3 is installed in a main chamber 1. The crucible 3 has a double structure in which an inner quartz crucible 3a and an outer graphite crucible 3b are combined.
[0036]
The support shaft 4 rotates and moves up and down the quartz crucible 3a. A heater 5 is arranged outside the crucible 3, and a heat insulating material 6 is arranged outside the heater 5 along the inside of the main chamber 1. Inside the quartz crucible 3a (outside the grown crystal 7), a radiation shield 8 that is effective for improving the pulling speed and suppressing generation of crystal defects is suspended.
[0037]
On the other hand, the pulling shaft 9 hangs down in the pull chamber 2 and holds the seed crystal at its lower end. The support shaft 4 rotates and moves the crucible 3 up and down. The heater 5 provided on the outer periphery of the crucible 3 is operated. Further, the lower end of the seed crystal is heated by another heater.
[0038]
In the method for growing a single crystal according to a preferred embodiment of the present invention, first, a raw material melt 10 is formed in a crucible 3 with the inside of a main chamber 1 of a furnace kept in a predetermined atmosphere. Next, the seed crystal is immersed in the raw material melt 10. Then, while rotating the pulling shaft 9, the seed crystal is pulled to grow the silicon single crystal 7 below the seed crystal. At this time, the crucible 3 is driven to rotate in the same direction as the pulling shaft 9 or in the opposite direction, and is driven upward as the growth proceeds so that the liquid level of the raw material melt 10 is kept constant.
[0039]
The growing crystal 7 is pulled in the order of a neck, a shoulder, a body, and a tail. As a result, a shoulder portion is formed below the neck portion, and the growth of the cylindrical body portion is started below the shoulder portion.
[0040]
After performing the body part growing process as described above, the pulling speed of the single crystal is once increased to 0.2 mm / min. After the temperature is lowered and the crystal diameter is kept constant (for example, maintained in this state within 15 minutes) while adjusting the power of the heater 5, the silicon single crystal 7 is cut off from the raw material melt 10.
[0041]
Alternatively, a tail portion is formed to a predetermined diameter, and the same operation as above is performed to cut off the silicon single crystal 7.
[0042]
The separation speed at that time was 200 mm / min. The above is desirable. In this case, the silicon single crystal 7 is separated more smoothly than the melt 10, and the shape of the solid-liquid interface becomes substantially M-shaped or inverted W-shaped when the distance c in FIG. It is separated as it is.
[0043]
Further, in this case, a thin film of the melt is formed on the cut end face of the silicon solid crystal, solidifies from the solid crystal side toward the cut end face, and no pressure is applied to the solid crystal due to volume expansion, and no dislocation occurs.
[0044]
In particular, in the case of a large-diameter silicon single crystal, the distance of c in FIG. 4 is set to 20 mm or less, and when there is one droplet portion 23, the melt 10 is depressed above the outer periphery of the single crystal 20 (that is, It is cut off smoothly from the concave portion 21) to the center without dislocation. If the distance c exceeds 20 mm, the portion raised from the liquid surface of the melt 10 due to surface tension rebounds at the time of separation and adheres to the tail end portion 20 of the single crystal, and the single crystal 20 is liable to be dislocated. Would.
[0045]
Example 1
The pulling of a silicon single crystal having a diameter of 400 mm was performed using the apparatus shown in FIG. The tail portion 20 of the silicon single crystal was squeezed to a diameter of 300 mm, and the pulling speed was once set to 0.4 mm / min. From 0.15 mm / min. And after 15 minutes, a cutting speed of 500 mm / min. And separated.
[0046]
FIG. 6 shows an X-ray topographic image near the dislocation-free separated end face.
[0047]
As can be seen from FIG. 6, it can be confirmed that the separated silicon single crystal has no dislocation.
[0048]
In the case of a large-diameter silicon single crystal, its outer peripheral portion solidifies quickly, but by setting the distance c to 20 mm or less and making the cut end face substantially M-shaped or inverted W-shaped, the crystal 7 Is smoothly performed from the outer peripheral portion to the inner peripheral portion, and is finally separated without dislocation by the droplet portion 23 formed at the center.
[0049]
Example 2
In pulling a silicon single crystal having a diameter of 400 mm, the tail is squeezed to a diameter of 300 mm, and the pulling speed is once set to 0.15 mm / min. And after 30 minutes, a cutting speed of 500 mm / min. And separated. The separation holding distance is 50 mm, and the length from the outermost peripheral portion of the separation end surface to the tip of the central projection is 8 mm.
[0050]
FIG. 7 shows an X-ray topographic image near the dislocation-free separated end face.
[0051]
As can be seen from FIG. 7, the separated silicon single crystal has no dislocation. By forming a thin film by suppressing the melt raised by the silicon solid crystal to a small amount at the time of cutting, the melt portion can be solidified from the solid crystal side to the cut end face, and a dislocation-free single crystal can be obtained.
[0052]
【The invention's effect】
According to the present invention, in pulling a large-diameter silicon single crystal, the tail step can be shortened or omitted, the yield can be improved, and the work load of the single crystal manufacturing step can be reduced. It is possible.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing dislocations caused by volume expansion.
FIG. 2 is a schematic diagram of dislocation-free separation.
FIG. 3 is a schematic view of the separation.
FIG. 4 is a schematic view of a tail end portion of a silicon single crystal manufactured by the single crystal manufacturing method of the present invention.
FIG. 5 is a schematic cross-sectional view of a crystal growing apparatus for carrying out the method for producing a single crystal of the present invention.
FIG. 6 is an X-ray topograph near a dislocation-free cut end face of a silicon single crystal manufactured by the single crystal manufacturing method of the present invention. One end face is shown by combining two graphs.
FIG. 7 shows an X-ray photograph image near a dislocation-free cut end face. About half of the end face is shown. It is symmetrical about the droplet part 23.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Main chamber 2 Pull chamber 3 Crucible 4 Support shaft 5 Heater 6 Insulation material 7 Growth crystal 8 Radiation shield 9 Pulling shaft

Claims (5)

In a silicon single crystal manufactured by the Czochralski method, an annular concave portion is formed on the tail end surface of the silicon single crystal along an outer peripheral portion, and a disk-shaped convex concentrically is formed inside the annular concave portion. A silicon single crystal, characterized in that a single droplet is formed at the center of the disk-shaped projection, and a projection-shaped droplet formed downward at the time of separation is formed. In a silicon single crystal manufactured by the Czochralski method, the tail end face of the silicon single crystal has a slope at the outer periphery of the single crystal, and an annular concave portion is formed inside the slope. A disc-shaped convex portion is formed concentrically inside the annular concave portion, and a protruding droplet portion formed downward at the time of separation at the center of the convex portion of the disc is formed. Silicon single crystal. The height difference from the uppermost part of the annular concave part to the lowermost part of the disk-shaped convex part excluding the liquid drop part is 20 mm or less, The characteristic according to any one of claims 1 to 2 characterized by things. Silicon single crystal. The silicon single crystal according to any one of claims 1 to 3, wherein a diameter of the disk-shaped convex portion is larger than a width of the annular concave portion. A method for producing a silicon single crystal by the Czochralski method, wherein when a silicon single crystal is separated from a raw material melt, a pulling speed is set to 0.2 mm / min. Below, and then the cutting speed is set to 200 mm / min. The method for producing a silicon single crystal according to claim 1, wherein:

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