JP5417735B2 - Method for growing silicon single crystal - Google Patents

Description

  The present invention relates to a method of pulling and growing a silicon single crystal from a silicon melt in a crucible by the Czochralski method (hereinafter referred to as “CZ method”), and particularly, in the process of growing a straight body portion of a silicon single crystal. The present invention relates to a method for growing a silicon single crystal when dislocation occurs.

  A single crystal growth method based on the CZ method is widely used to manufacture a silicon single crystal that is a material of a semiconductor material silicon wafer. The growth of a silicon single crystal by this CZ method is generally performed as follows. In the pulling apparatus in a reduced pressure atmosphere, the polycrystalline silicon raw material filled in the quartz crucible is heated and melted by a heater surrounding the quartz crucible. When the silicon melt is formed in the quartz crucible, the seed crystal suspended above the quartz crucible is lowered and immersed in the silicon melt. From this state, the seed crystal and the quartz crucible are rotated in a predetermined direction, and the seed crystal is gradually pulled up, whereby a silicon single crystal is grown below the seed crystal.

  Further, in recent years, in order to efficiently grow a silicon single crystal having no grown-in defects such as COP and dislocation clusters, a heat shield surrounding the periphery of the silicon single crystal being pulled is provided above the crucible. A pulling device having a water-cooled body that surrounds the periphery of the single crystal inside the heat shield is often used (see, for example, Patent Documents 1 and 2).

  In the growth of a silicon single crystal, a conical shoulder portion having a diameter gradually increased from a neck portion formed immediately below the seed crystal to a desired diameter is formed, and then a desired diameter to be handled as a product for a silicon wafer. In addition, an inverted conical tail portion having a diameter gradually decreased from the straight body portion to prevent introduction of dislocations at the final stage of growth is formed, and a silicon single unit is formed at the lower end of the tail portion. The crystal is separated from the silicon melt. And the silicon melt which was not crystallized remains in the quartz crucible after pulling up the silicon single crystal.

  At this time, if there is a large amount of silicon melt remaining in the quartz crucible (hereinafter referred to as “residual melt”), due to the difference in coefficient of thermal expansion between silicon and the quartz crucible, the remaining solidified from the surface thereafter. Due to the solidification and expansion of the melt, the quartz crucible may be damaged, or the carbon crucible containing the quartz crucible and the heater disposed on the outside thereof may be damaged. For this reason, in actual operation, the silicon single crystal is grown so that the residual melt in the quartz crucible is as small as possible (see, for example, Patent Document 3).

JP 2002-128589 A JP 2001-220289 A JP-A-5-70280 (paragraphs [0004] to [0005])

  By the way, in the growth of a silicon single crystal, dislocation may occur due to foreign matters mixed in the crystal or poor control of pulling operation parameters.

  In general, when dislocations occur in the growing silicon single crystal, it is known that the crystal part after the dislocations occurs will be polycrystallized, and the dislocations occur It is known that slip dislocations extend from above to a crystal part that is not dislocated and the extension length extends to the diameter of the silicon single crystal that is generally pulled up. For this reason, normally, when tailing a silicon single crystal that is not dislocation-oriented, the tail portion having a length longer than the diameter of the single crystal to be pulled up is assumed, assuming that dislocation formation occurs during tail-drawing. Has been done.

  On the other hand, when dislocations occur in the growing single crystal, the healthy crystal part (straight barrel part) grown up to that point is utilized, and the above-mentioned quartz crucible breakage and carbon crucible damage are prevented. For this reason, the growth of a single crystal is continued even after the occurrence of dislocations, and the silicon single crystal is grown so that the remaining melt in the quartz crucible becomes as small as possible.

  However, dislocation-induced silicon single crystals cause slip dislocation extension regions caused by dislocations and dislocations during pulling in the pulling device, removal from the pulling device, or during cutting. Thereafter, cracks are likely to occur in the polycrystallized sites, and cracks are particularly likely to occur in the slip dislocation extension sites. This is presumably because these crystal parts are lower in strength than normal single crystal parts, and the residual stress in the crystal is increased by being rapidly cooled by a water-cooled body. The cracked silicon single crystal breaks or ruptures due to the progress of the crack, causing a serious accident.

  The present invention has been made in view of the above problems, and even when dislocation is generated in the process of growing the straight body portion, at the time of lifting in the lifting device, at the time of taking out from the lifting device, or at the time of cutting processing An object of the present invention is to provide a method for growing a silicon single crystal that can prevent the silicon single crystal from being broken or ruptured.

In order to achieve the above object, the present inventor has examined the growth state of the silicon single crystal in detail, and as a result, unlike the conventional operation, when dislocation occurs in the straight body portion, the constriction is immediately performed. Transition to the formation of an inverted frustoconical tail having a round shape and a rounded outer periphery, and the tail is formed shorter than when no dislocation occurs during crystal growth. It was found that the silicon single crystal in which dislocations are generated does not crack when separated, and is effective in preventing the silicon single crystal from being broken or ruptured.

The present invention is based on such knowledge, and in the method for growing a silicon single crystal by the CZ method, when dislocation occurs in the process of growing the straight body of the silicon single crystal, the tapered shape is immediately formed. Then, the inverted frustoconical tail portion with a rounded outer periphery is formed, and the length of the tail portion is shortened compared to the case where dislocation does not occur during crystal growth. It is characterized by being separated from the silicon melt in the crucible.

  “When dislocations occur” as used herein refers to occurrence of dislocations by visually or optically monitoring a growing single crystal, for example, occurring in a single crystal growing in actual operation When the crystal habit line is monitored, it means when the crystal habit line disappears due to polycrystallization. Further, “immediately” means that as soon as a dislocation is found in monitoring during the growth of a single crystal.

At this time, it is preferable that the length from the generation | occurrence | production position of dislocation in the said straight body part to the lower end of the said tail part shall be 100 mm or less. In addition, by making the tail part into a tapered shape and an inverted frustoconical shape with a rounded outer periphery , the total amount of the tail part can be reduced as much as possible, and cracks in the silicon single crystal Can be prevented . Also, formation of the tail portion increases the temperature of the silicon melt by increasing the output of the heater for heating the crucible, it is preferably carried out while suppressing an increase of pulling speed. In the present invention, since the silicon single crystal that has already undergone dislocation is tail-squeezed, it is not necessary to consider the occurrence of dislocation during tail-squeezing, and no matter what the length of the tail portion is reduced. Does not cause any problems.

  In particular, such a configuration can be used for single crystal growth in which a silicon single crystal being pulled is cooled by a water-cooled body disposed so as to surround it.

  According to the method for growing a silicon single crystal of the present invention, the thermal stress remaining in the silicon single crystal can be relaxed, and the generation of cracks in the silicon single crystal can be prevented. As a result, it becomes possible to prevent the silicon single crystal from being broken or ruptured.

Hereinafter, an embodiment of the method for growing a silicon single crystal of the present invention will be described in detail.
FIG. 1 is a longitudinal sectional view showing a configuration of a pulling apparatus to which a method for growing a silicon single crystal according to an embodiment of the present invention is applied. As shown in the figure, a crucible 2 is disposed in the center of a chamber 1 that forms the outline of the lifting device. The crucible 2 has a double structure, and is composed of an inner quartz crucible 2a and a graphite crucible 2b fitted on the outer side. The crucible 2 has a graphite crucible 2b fixed to the upper end portion of the support shaft 3, and rotates in the circumferential direction or moves up and down in the axial direction in accordance with the rotational drive and lift drive of the support shaft 3.

  A resistance heating type heater 4 surrounding the crucible 2 is arranged outside the crucible 2, and a heat insulating cylinder 5 is arranged along the inner surface of the chamber 1 further outside. The heater 4 melts the polycrystalline silicon raw material filled in the crucible 2, whereby a silicon melt 6 is formed in the crucible 2.

  On the other hand, a wire 7 as a lifting shaft is suspended above the crucible 2. The wire 7 is rotationally driven by a pulling mechanism (not shown) provided at the upper end of the chamber 1 and is driven up and down in the axial direction. A seed crystal 8 is attached to the lower end of the wire 7. By immersing the seed crystal 8 in the silicon melt 6 in the crucible 2 and driving the wire 7 to gradually raise the seed crystal 8 while rotating it, a silicon single crystal 9 is grown below the seed crystal 8. The

  Above the crucible 2, a cylindrical graphite heat shield 10 surrounding the periphery of the silicon single crystal 9 being pulled is provided. The heat shield 10 includes a heat insulating material inside, and plays a role of blocking radiant heat from the silicon melt 6 and the heater 4 in the crucible 2 with respect to the silicon single crystal 9 being pulled up.

  A cylindrical water-cooled body 11 surrounding the periphery of the silicon single crystal 9 being pulled is provided inside the lower part of the heat shield 10. The water-cooled body 11 is made of, for example, a metal having good thermal conductivity such as copper, and is forcibly cooled by cooling water that is circulated inside. The water-cooled body 11 plays a role of accelerating the cooling of the high-temperature portion by disposing it so as to surround the high-temperature portion immediately after solidification of the silicon single crystal 9 being pulled.

  Next, in the single crystal growth using such a pulling apparatus, an example of operation when dislocation occurs in the straight body growth process will be described.

  FIG. 2 is a diagram schematically showing steps in the method for growing a silicon single crystal according to an embodiment of the present invention. As shown in FIG. 5A, when growing the silicon single crystal 9 from the silicon melt 6 in the crucible 2, dislocations are formed in the growing process of the straight body portion 9b after the shoulder portion 9a is formed. Suppose that it occurred. In the figure, the dislocation generation position D is indicated by a broken line. In the present embodiment, the occurrence of dislocation can be determined by visually or optically monitoring the crystal habit line during the growth of the straight body portion 9b.

  When it is determined that dislocations have occurred in the straight body portion 9b of the silicon single crystal 9 being pulled, the growth conditions are immediately switched to move to the formation of the tail portion 9c to form the tail portion 9c (see FIG. (See (b)). At this time, in order to shift to the formation of the tail portion 9c, an operation of instantaneously and greatly increasing the output (power) of the heater 4 is performed. Thereby, since the emitted-heat amount of the heater 4 increases rapidly, the temperature of the silicon melt 6 in the crucible 2 rises in a short time. By such an operation, the silicon single crystal 9 is successively reduced in diameter and a tail portion 9c is formed.

  Then, as shown in FIG. 5C, the silicon single crystal 9 is naturally separated from the silicon melt 6 in the crucible 2 in a short time after the transition to the formation of the tail portion 9c, and the outer periphery is rounded. A tapered tail portion 9c having a generally inverted truncated cone shape is formed.

  In the silicon single crystal 9 obtained in this way, slip dislocations extend toward the crystal portion above the dislocation occurrence position D in the straight body portion 9b, and the tail portion 9c extends from the dislocation formation occurrence position D. Although the region of the length L to the lower end of the film is polycrystallized, no cracks are generated in these crystal parts. This is because the length L from the position of occurrence of dislocation to the lower end of the tail portion is shortened, so that the volume of this crystal part is reduced, so that the thermal stress remaining in the slip dislocation generation region and the polycrystalline region is reduced. By being relaxed. As a result, breakage and rupture of the silicon single crystal 9 can be prevented.

  If a large amount of residual melt remains in the crucible 2, the crucible 2 (quartz crucible 2a) may be damaged if it is left as it is. For such a situation, for example, before the residual melt is solidified, the single crystal is grown again, or the polycrystalline silicon raw material is additionally charged into the crucible 2 where the residual melt remains to be melted. This can be solved by applying a so-called multiple pulling method in which a single crystal is grown from a silicon melt based on the residual melt and the polycrystalline silicon raw material.

  FIG. 3 is a diagram schematically showing the correlation between the formation time and formation length of the tail portion and the output of the heater, and FIG. 4 shows the correlation between the formation time and formation length of the tail portion and the temperature of the silicon melt. It is a figure shown typically. These FIG. 3 and FIG. 4 show the situation when forming the tail part in this embodiment due to the occurrence of dislocation in the straight body part by a solid line, and the situation when forming a normal tail part by a dotted line. Show. 3 and 4, the time when the transition to the formation of the tail portion is indicated by a white circle, and the time when the silicon single crystal is separated from the silicon melt is indicated by a black circle.

  As shown in FIGS. 3 and 4 above, when forming the tail portion due to the occurrence of dislocation in the straight body portion, the output of the heater is greatly increased instantaneously during the transition of the tail portion formation, The temperature of the silicon melt in the crucible rises in a short time. For this reason, since the silicon single crystal is separated from the silicon melt in a short time (for example, about 20 to 60 minutes), the formation length of the tail portion is shortened.

  On the other hand, when the tail portion is formed by normal single crystal growth, the output of the heater is gradually increased from the transition to the tail portion formation, thereby gradually increasing the temperature of the silicon melt in the crucible over a long period of time. . For this reason, since the silicon single crystal is separated from the silicon melt after a long time (for example, about 2 to 8 hours) has elapsed, the formation length of the tail portion becomes long.

  FIG. 5 shows the relationship between the length L from the occurrence position D of dislocations to the lower end of the tail portion and the occurrence of cracks in a silicon single crystal in which dislocations occurred during the growth process of the straight barrel portion. FIG. This figure shows that when a silicon single crystal having a diameter of 200 mm is grown, the length L from the occurrence position D of the dislocation to the lower end of the tail portion is changed, and the slip extension site and polycrystal produced by the dislocation The result of having observed the site | part visually is shown. From the results shown in the figure, when the length L from the dislocation occurrence position D to the lower end of the tail portion is 100 mm or less, cracks do not occur in the slip extension portion and the polycrystalline portion caused by the dislocation.

  Therefore, in the present embodiment, dislocation occurs in the process of growing the straight body portion, and when the tail portion is immediately formed, the length L from the occurrence position D of the dislocation to the lower end of the tail portion is 100 mm or less. The output of the heater is adjusted so that In particular, when a silicon single crystal having a diameter of 200 mm is grown, in consideration of safety, the length L from the dislocation generation position D to the lower end of the tail portion is preferably set to 70 to 80 mm or less. When growing a silicon single crystal having a larger diameter and a diameter of 300 mm, since the volume increases, the length from the dislocation occurrence position D to the lower end of the tail portion is further considered in consideration of safety. L is preferably 50 mm or less.

  Furthermore, when forming the tail portion, in addition to the adjustment of the heater output, it is possible to adjust the pulling rate of the silicon single crystal sequentially to decrease the crystal diameter. However, if the pulling speed is increased too much, the tail portion becomes longer and the length L from the dislocation generation position D to the lower end of the tail portion becomes longer, which may cause cracking. It is preferable to raise it little by little from the previous pulling speed.

  Also, in single crystal growth using a water-cooled body, when the silicon single crystal was separated from the silicon melt and then pulled up at a high speed, the slip-extended portion and the polycrystalline portion caused by dislocation were placed in the water-cooled body. Since it passes through the region at high speed, the thermal stress remaining in these crystal parts increases, and cracks are likely to occur. For this reason, until the lower end of the tail part of the silicon single crystal exceeds the arrangement area of the water-cooled body, the pulling speed is suppressed to 7 mm / min or less, and after exceeding the arrangement area of the water-cooled body, the pulling speed is set to 12 mm / min or less. It is preferable to ensure the above.

  In order to confirm the effect of the method for growing a silicon single crystal of the present invention, tests shown in the following examples were conducted.

  In the test of Example 1, a silicon single crystal was grown using the pulling apparatus shown in FIG. 1 so that the target diameter of the straight body portion was 200 mm and the target length of the straight body portion was 1700 mm. At that time, the crucible was filled with a silicon raw material, and boron (B) as a dopant was added so as to obtain a p-type electrical resistivity. The inside of the pulling apparatus was put under a reduced-pressure atmosphere of argon, and both raw materials were melted by heating with a heater to form a silicon melt. The seed crystal was adjusted to the silicon melt, and the pulling was started while rotating the crucible and the pulling shaft. After forming the neck portion with the crystal orientation of <100>, the shoulder portion was formed, and then the shoulder was changed to grow the straight body portion of the target diameter.

  In Example 1, since the dislocation occurred at the position of 1110 mm before the length of the straight body part reached the target length, the process immediately shifted to the formation of the tail part. At this time, the heater output was instantaneously increased by 15 kW. The pulling speed was maintained as it was before the transition to tail portion formation. As a result, the temperature of the silicon melt increased, the diameter of the single crystal gradually decreased, and a narrow tail portion with a rounded outer periphery was formed. In about 30 minutes after the transition to the formation of the tail portion, the length from the dislocation generation position to the lower end of the tail portion is about 30 mm, and by raising the pulling speed at this stage, the silicon single crystal becomes silicon. Naturally separated from the melt.

  With respect to the silicon single crystal thus obtained, slip extension sites and polycrystalline sites caused by dislocation were observed. As a result, there was no crack in these crystal parts, and the silicon single crystal was not broken or ruptured.

  In the test of Example 2, the same pulling apparatus and test conditions as those of Example 1 were used, and a silicon single crystal was grown with the target diameter of the straight body part being 200 mm and the target length of the straight body part being 1700 mm. .

  In Example 2, since the dislocation occurred at the position of 1270 mm before the length of the straight body part reached the target length, the process immediately shifted to the formation of the tail part. At this time, the temperature of the silicon melt was slightly lower than that in Example 1, and the output of the heater was instantaneously increased by 15 kW. The pulling speed was slightly increased from the speed before the transition to tail portion formation. As a result, in about 40 minutes after the transition to the formation of the tail portion, the length from the dislocation generation position to the lower end of the tail portion is about 35 mm, and the silicon single crystal was naturally separated from the silicon melt. .

  The silicon single crystal thus obtained was not cracked, and the silicon single crystal was not broken or ruptured.

  In the test of Example 3, a silicon single crystal was grown using the same pulling apparatus and test conditions as in Example 1 above.

  In Example 3, since the dislocation occurred at the position of 1150 mm before the length of the straight body part reached the target length, the process immediately shifted to formation of the tail part to form the tail part. Then, the silicon single crystal separated from the silicon melt is continuously pulled up at a pulling speed of 5 mm / min until the lower end of the silicon crystal exceeds the arrangement area of the water-cooled body, and further pulled up to the take-out area at a pulling speed of 9 mm / min. It was.

  The silicon single crystal thus obtained was not cracked, and the silicon single crystal was not broken or ruptured.

  The method for growing a silicon single crystal according to the present invention does not cause a crack in a dislocation silicon single crystal, and can prevent the silicon single crystal from being broken or ruptured. Therefore, the present invention is an extremely useful technique for producing a silicon single crystal by the CZ method.

It is a longitudinal cross-sectional view which shows the structure of the pulling apparatus with which the growth method of the silicon single crystal which is one Embodiment of this invention is applied. It is a figure which shows typically the process in the growth method of the silicon single crystal which is one Embodiment of this invention. It is a figure which shows typically the correlation with the formation time and formation length of a tail part, and the output of a heater. It is a figure which shows typically the correlation with the formation time and formation length of a tail part, and the temperature of a silicon melt. The figure which summarized the relationship between the length L from the occurrence position D of dislocations in the straight body part to the lower end of the tail part and the occurrence of cracks for silicon single crystals in which dislocations occurred during the growth process of the straight body part It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chamber 2 Crucible 2a Quartz crucible 2b Graphite crucible 3 Support axis | shaft 4 Heater 5 Thermal insulation cylinder 6 Silicon melt 7 Wire (lifting axis)
8 Seed crystal 9 Silicon single crystal 9a Shoulder portion 9b Straight body portion 9c Tail portion 10 Thermal shield 11 Water-cooled body D Position of occurrence of dislocation L Length from the position of occurrence of dislocation to the lower end of tail portion

Claims (4)

In the method of growing a silicon single crystal by the Czochralski method,
When dislocations occur in the growth process of the straight body of a silicon single crystal, immediately form a tapered portion with an inverted truncated cone shape with a rounded outer periphery , and the formation length of the tail portion A method for growing a silicon single crystal, wherein the silicon single crystal is separated from the silicon melt in the crucible by shortening the length compared to the case where dislocations do not occur during crystal growth.   2. The method for growing a silicon single crystal according to claim 1, wherein the length from the occurrence of dislocation in the straight body portion to the lower end of the tail portion is 100 mm or less. Formation of the tail portion increases the temperature of the silicon melt by increasing the output of the heater for heating the crucible, to claim 1 or 2, characterized in that while suppressing the amount of increase of pulling speed A method for growing a silicon single crystal as described. The silicon in the pulled single crystal, the method for growing a silicon single crystal according to any one of claims 1 to 3, characterized in that cooling by arranged water-cooling structure so as to surround it.

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