JP4640796B2 - Method for producing silicon single crystal - Google Patents

Description

  The present invention relates to a method for manufacturing a silicon single crystal, and more particularly, to a method for manufacturing a silicon single crystal in which the strength of a magnetic field applied to a melt is changed according to the growth process when growing the silicon single crystal.

  In growing a silicon single crystal using the Czochralski method (hereinafter referred to as CZ method), a crucible is filled with a melt raw material, heated and melted to form a melt, and a seed crystal is brought into contact with the melt. The seed crystal is pulled up to grow a silicon single crystal.

  When a silicon single crystal is grown by the CZ method, oxygen dissolved in the melt from the crucible is taken into the grown silicon single crystal. Since the silicon single crystal incorporating oxygen has improved mechanical strength, there is a tendency that slip, warpage, etc. during heat treatment are less likely to occur, and also for the formation of BMD (Bulk Micro Defect) that provides gettering action. Known to be useful.

  However, if the oxygen concentration in the silicon single crystal is not uniformly controlled in the surface inner diameter direction, the gettering effect varies within the surface. Therefore, when growing a silicon single crystal for a semiconductor device, it is an important issue to make the oxygen concentration distribution in the crystal uniform in the surface inner diameter direction.

  In order to achieve such concentration control and in-plane uniformity of concentration distribution, the Czochralski method (hereinafter referred to as MCZ) in which a magnetic field is applied to the melt is widely employed.

  For example, in Patent Document 1, in order to improve the uniformity of the oxygen concentration not only in the crystal growth direction but also in the radial direction, the lower part region in the crucible is a silicon solid layer and the upper part region is a molten layer, MCZ has been proposed in which a magnetic field of 100 Oe (Oersted) to 500 Oe is applied to the molten layer.

  In Patent Document 2, in order to improve the single crystallization rate, at the start of pulling of the semiconductor single crystal, the vertical magnetic field center is shifted downward from the solid-liquid interface between the semiconductor single crystal and the semiconductor melt. A magnetic field is applied with a magnetic field strength of Gauss or higher, and the magnetic field center in the vertical direction is moved to a position where the temperature oscillation of the surface of the semiconductor melt obtained in advance is minimized as the semiconductor melt decreases. The above method has been proposed.

However, in the CZ method and the MCZ method, when the seed crystal is brought into contact with the melt, heat shock dislocation occurs due to the thermal shock. If the dislocations generated here propagate to the straight body portion which becomes the wafer portion, the single crystallization rate is lowered. Therefore, in recent years, propagation of heat shock dislocation has been prevented by growing a dash neck portion whose diameter is reduced to 3 mm or less by the dash neck method. With the recent increase in the diameter of grown single crystals, the presence of the dash neck portion may cause a fall accident of the silicon single crystal due to breakage or the like.
JP-A-7-277776 JP 2001-89289 A

  The present invention has been made in consideration of the above-described circumstances, and is capable of forming an oxygen concentration distribution in a silicon single crystal uniformly in a plane and is easily grown by eliminating heat shock dislocations. An object of the present invention is to provide a method for producing a silicon single crystal capable of increasing the single crystal ratio.

In order to achieve the above-described object, a method for producing a silicon single crystal according to the present invention is a method for producing a silicon single crystal by the Czochralski method in which a magnetic field is applied to a melt in a crucible, A step of growing a neck portion by bringing a crystal into contact, a step of growing the neck portion after expanding the neck portion to a desired diameter, and a step of growing the enlarged portion, and maintaining the desired diameter after growing the enlarged portion. While the step of growing the straight body part and the step of separating the straight body part from the melt, the magnetic field strength is in the range of 200 to 1000 Gauss from the time of growing the neck part to before the growth of the straight body part. A magnetic field is applied to the melt, and the magnetic field strength is gradually reduced from 200 to 400 gauss immediately after the straight body part is grown to immediately after the straight body part length is 150 to 250 mm. , Magnetic field strength 350 A magnetic field is applied to the melt in a range of ˜500 gauss.

  According to the silicon single crystal pulling method according to the present invention, the oxygen concentration in the silicon single crystal can be formed at an optimum concentration and the concentration distribution can be uniformly formed in the plane.

  Hereinafter, an embodiment of a method for producing a silicon single crystal according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a conceptual diagram of a silicon single crystal pulling apparatus used in the method for producing a silicon single crystal according to the present invention.

  The silicon single crystal pulling apparatus 1 fills a quartz crucible 2 with a melt raw material, and heats and melts the melt raw material with a heater 3 arranged around the quartz glass crucible 2 to obtain a melt M.

Thereafter, the magnetic field center L connecting the centers of the two coils existing outside the chamber C in this state is 500 gauss by the superconducting magnet 4 in which the coil is disposed at a height near the liquid surface S of the silicon melt M. The quartz glass crucible 2 is rotated while applying a magnetic field of ˜1000 gauss, the seed crystal s attached to the chuck 6 provided on the wire 5 is lowered and brought into contact with the silicon melt M, and the pulling neck portion In is grown. Then, the expanded diameter portion Ic is continuously grown.

When a magnetic field is applied to the silicon melt M, the flow at the crucible wall is suppressed and natural convection is weakened. When growing the neck portion In and the enlarged portion Ic having relatively small diameters, if the magnetic field strength is less than 500 gauss, the flow in the melt is not stable, and the single crystallization rate is significantly reduced. Further, when the magnetic field strength exceeds 1000 gauss, there arises a problem that the convection of the melt is disturbed. For this reason, it is preferable to set the magnetic field strength within a range of 500 gauss to 1000 gauss when growing the neck portion In and the crown portion Ic.

  After the growth of the crown portion Ic, the straight body portion Is is subsequently grown while controlling the diameter to a desired diameter using the rotation speed of the quartz crucible 2, the pulling speed of the single crystal, the heater 3 and the like. In this straight body part growing process, forced convection becomes large immediately after the straight body part Is is grown, that is, from 0 mm to 150 to 250 mm (hereinafter referred to as the front part of the straight body part), because a large amount of the melt M exists. When a strong magnetic field is applied, convection is generated and disturbed in the melt, so that the magnetic field is changed to a range of 200 to 400 gauss, a low magnetic field is applied, and the straight body part Is is grown. As a result, the melt is stabilized, and the oxygen concentration distribution of the straight body portion Is can be uniformly formed in the radial direction plane.

  If the magnetic field strength in the range from 150 to 250 mm immediately after the straight body portion Is growth is less than 200 gauss, the convection of the melt from the quartz glass crucible to the crystal becomes too strong, leading to deformation of the single crystal and being stable. I can't hope to raise. If the magnetic field intensity exceeds 400 gauss, forced convection increases as described above, and convection is generated and disturbed, so that the oxygen concentration distribution cannot be uniformly formed in the plane.

  When the growth to 150-250 mm in length is finished in the straight body part, it becomes the latter part of the straight body part, and when the remaining amount of the melt is reduced, the magnetic field is slightly increased from the low magnetic field of 200-400 gauss applied so far. Apply a magnetic field.

  The reason for raising the magnetic field again is that if the amount of residual melt decreases after the straight body part, the area of the low temperature part of the melt surface increases, so the flow from the crucible wall to the crystal through the free surface is reversed. The flow changes from the inside of the melt toward the crystal. This complicates the flow inside the melt, and the flow toward the crucible wall due to crystal rotation interferes with the flow from the inside toward the crystal, causing vortices near the boundary between the crystal periphery and the free surface. Arise. Since oxygen in this vicinity evaporates more than necessary on the free surface, resulting in a decrease in the oxygen concentration at the outer periphery of the crystal, it is necessary to increase the magnetic field to eliminate such disturbance of the melt.

Accordingly, a strong magnetic field is applied from the time of neck growth to before the straight body part is grown , that is, in a state where the remaining amount of the melt is large. It is possible to grow a silicon single crystal having a uniform oxygen concentration in the direction of the inner diameter of the surface by applying a low magnetic field by lowering and weakening it, and further raising the magnetic field slightly after the growth of the straight body portion.

  Further, as described above, the inventor gradually applies a strong magnetic field when growing the neck portion In and the enlarged diameter portion Ic, and gradually increases the magnetic field from a strong magnetic field to a low magnetic field within a range of 150 to 250 mm immediately after the straight body portion Is is grown. As a result of the reduction, the above-mentioned secondary effect that the propagation of the heat shock dislocation was suppressed and the single crystallization rate was improved was found. This is presumably because the convection of the melt changes due to the change in the magnetic field strength, and the heat shock dislocation propagated to the enlarged diameter portion Ic disappears there.

  According to the above-described embodiment, the oxygen concentration distribution in the silicon single crystal can be uniformly formed in the plane, and the single crystal ratio of the grown silicon single crystal can be easily increased by eliminating the heat shock dislocation. A method for producing a silicon single crystal that can be realized is realized.

  The test was conducted using the single crystal pulling apparatus shown in FIG. First, a melt raw material was filled in a crucible, and heated and melted with a heater to obtain a melt. After the melt was formed, a magnetic field of 800 gauss was applied, and the center of the magnetic field connecting the centers of the two coils was set at a height of 30 mm from the liquid surface S of the silicon melt M as needed. Next, the seed crystal was brought into contact with the melt and pulled up to grow a neck portion having a minimum diameter of 5 mm to a length of 200 mm, and then expanded to a diameter of 315 mm to form an enlarged portion.

  After forming the enlarged diameter part, the diameter of the straight body part is controlled immediately after the start of straight body part growth, and the length of the straight body part is increased immediately after the start of straight body part growth by gradually changing the 800 gauss magnetic field strength to 200 gauss. The magnetic field strength was reduced by 200 gauss to the part to grow 200 mm. When the growth of the straight body part exceeded 200 mm in length, the magnetic field intensity was changed to 400 gauss, and the straight body part was grown to a length of 1400 mm. Thereafter, the silicon single crystal grown from the melt was cut off.

Test 1: The relationship between the magnetic field strength and the single crystallization rate during neck portion growth was examined, and the results are shown in FIG. When it is 200 gauss or more , the single crystallization rate is 70% or more, but when it is less than 200 gauss, it is divided by 70%, and when it is 100 gauss, it decreases to 60%.

  Test 2: At the time of growing the straight body portion (after the crystal length of 50 mm), the magnetic field strength was changed and the in-plane variation of the oxygen concentration was examined. The results are shown in FIG. The single crystallization rate is good at 200 to 400 gauss, but poor at 800 gauss, and the in-plane distribution is good at 100 gauss, but as can be seen from Test 1, the single crystallization rate decreases.

Reference Example 1 : When the length of the crystal body was raised by 200 mm, the magnetic field strength was changed and the in-plane variation of the oxygen concentration was examined. The results are shown in FIG. At 200 gauss, the oxygen concentration is constant and uniform in the plane, while at 800 gauss, the oxygen concentration is unstable and non-uniform in the plane.

Test 3 : When pulling up a single crystal by applying a magnetic field, deformation may occur in the single crystal near a crystal solidification rate of 0.42, and the degree of crystal deformation was examined by changing the magnetic field strength. The results are shown in FIG. Considering the number of occurrences of crystal deformation, the magnetic field strength is preferably 350 gauss or more, and considering the oxygen in-plane distribution, it is preferably 500 gauss or less.

Reference Example 2 : Using a silicon single crystal pulling method according to the present invention, a silicon single crystal having a diameter of 300 mm is pulled, the magnetic field strength is constant at 800 gauss in the neck and crown growing step, and 0 to 0 in the straight barrel growing step. As a result of changing from 800 to 200 gauss at 50 mm, and further changing the range of the magnetic field strength to 800 gauss again after the straight body length of 200 mm, the single crystal crystallization rate was 70% of the conventional value. Improved to 95%. In addition, when a magnetic field was applied constantly within the range of 200 to 400 gauss in the straight body part growing step, the in-plane variation rate of the oxygen concentration was 1.5% or less, and good results were obtained.

The conceptual diagram of the pulling-up apparatus used for the manufacturing method of the silicon single crystal which concerns on this invention. The test result figure which shows the relationship between the magnetic field intensity at the time of the neck part growth in single crystal pulling, and a single crystallization rate. The test result figure which shows the relationship between magnetic field intensity and oxygen concentration in-plane dispersion | variation. The test result figure which shows the relationship between the crystal diameter and oxygen concentration using the silicon single crystal pulling method which concerns on the reference example 1 of this invention. The test result figure which shows the relationship between magnetic field strength and a crystal deformation generation | occurrence | production degree.

DESCRIPTION OF SYMBOLS 1 Silicon single crystal pulling apparatus 2 Quartz glass crucible 3 Heater 4 Superconducting magnet 5 Wire 6 Chuck In Neck part Ic Crown part Is Straight trunk part M Silicon melt

Claims (1)

A method for producing a silicon single crystal by the Czochralski method in which a magnetic field is applied to a melt in a crucible, a step of bringing a seed crystal into contact with the melt to grow a neck portion, and after growing the neck portion, Expanding the diameter-enlarged portion by expanding to a desired diameter, growing the straight-body portion while maintaining the desired diameter after growing the expanded-diameter portion, and removing the straight-body portion from the melt A step of separating, from the time of growing the neck portion to before growing the straight body portion, a magnetic field is applied to the melt in a magnetic field strength range of 500 to 1000 gauss, and the length of the straight body portion is 150 to immediately after the straight body portion is grown. Up to 250 mm, the magnetic field strength is gradually reduced to a magnetic field strength of 200 to 400 gauss, and further, a magnetic field is applied to the melt in a range of a magnetic field strength of 350 to 500 gauss after a straight body length of 150 to 250 mm. Silicon single Crystal production method.

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